Below is an alphabetical list of terms commonly used in DanZan Ryu Jujitsu. To skip to a particular letter, click below. A PDF version of this glossary, which also includes the kanji and additional details, can be downloaded here.

Numerals | Belt ranks | Notes


age rising
age zuki rising punch
age uke rising block
ai harmony; join; fit
aiki aligning one's ki with that of an opponent1; literally, "harmonized inner energy"
aikido martial art derived from aiki jujitsu but which places more emphasis on spiritual development; founded by Morihei Ueshiba in the early 20th century
aiki jujitsu style of juijtsu which places emphasis on aiki
ashi foot; leg; synonmous with soku
ashi guruma leg wheel; throw in judo
ashi gyaku legscrew; literally, "leg torutre"
ashi hishigi leg crush
ashi kubi ankle; literally, "neck of the leg"
ashi kubi hishigi ankle crush
ashi waza foot and leg techniques
atemi striking the body
atemi waza body-striking techniques


ba horse
bajitsu horsemanship; literally, "horse techniques"
barai spelling of harai when following another word
basami spelling of hasami when following another word
bo long staff
bojitsu art of the long staff
bokken wooden sword used in kendo and kenjitsu
bu military; martial
budo martial arts of late medieval and post-medieval Japan emphasizing spiritual, health, and sport aspects over combat and self-defense; literally, "martial way"; compare to bujitsu
budokai martial way organization
bunkai application of form
bushi warrior class of medieval Japan; also, a member of this class (synonymous with samurai2)
bushido unwritten moral and ethical code of conduct practiced by the bushi; similar to European chilavry; literally, "way of the warrior"
bujitsu fighting arts of the warrior class of medieval Japan; literally, "martial techniques" or "martial arts"; compare to budo


choku zuki straight punch
chuan fa (Chinese) fist way; kung fu; synonymous with kempo
chudan middle (of body); torso level


dachi spelling of tachi when following another word
dan degree or step; in Japanese martial arts, used for black belt ranks (see belt ranks)
daisho the two swords worn by the samurai: the katana and wakizashi; literally, "long and short"
de advanced; forward
de ashi barai forward foot sweep; throw in judo
denzook no count
deshi student; disciple
do way
dojo exercise hall; the place where one practices the martial arts
dori spelling of tori when following another word


ebi lobster; shrimp; prawn
ebi jime lobster choke
eku oar, used as a weapon in Okinawan karate
empi elbow; literally, "monkey arm", but considered synonymous with hiji in Japanese martial arts
empi uchi elbow strike
eri lapel; collar


fudo dachi rooted stance
fumi step on; tread on
fumikomi stepping into; stomping
fumikomi geri stomping kick
Funakoshi, Gichin father of Japanese karate, in particular, Shotokan


gake spelling of kake when following another word
ganmen face
ganmen shuto face-level knife-hand
ganmen shuto uchi face-level knife-hand strike
garami spelling of karami when following another word
gari reap; reaping
gatame spelling of katame when following another word
gaeshi spelling of kaeshi when following another word
gedan lower; waist-level or below
gedan barai uke low sweeping block
gedan haitto lower ridge-hand
gedan juji uke lower X-block
gedan shuto uke lower knife-hand block
geri spelling of keri when following another word
gi uniform for practicing martial arts
go five (see numerals)
godan fifth degree; fifth degree black belt (see belt ranks)
gohon five long cylindrical objects
gohon nukite five-finger spear-hand strike
gokyu fifth class (see belt ranks)
goshi spelling of koshi when following another word
guruma spelling of kuruma when following another word
gyaku 1. reverse; opposite; synonymous with saka; e.g., gyaku zuki
2. torture; tyranny; cruelty; oppression; e.g., ashi gyaku
gyaku zuki reverse punch (opposite-side hand and leg)
gyaku juji jime reverse cross choke


ha 1. edge (of a sword)
2. wing; e.g., kataha jime
hachi eight (see numerals)
hachidan eigth degree; eigth degree black belt (see belt ranks)
hachiji the kanji hachi
hachiji dachi open leg stance; literally, the stance where the feet are in the shape of the kanji hachi
hachimachi towel used as a headband
hadaka naked; nude; bare
hadaka jime naked choke
hadari left (side)
hai 1. yes
2. back; behind; e.g., haito
haishu back of the hand
haishu uchi back hand strike
haisoku instep; literally, "back of foot"
haisoku geri instep kick
haito ridge-hand (thumb side of hand); literally, "back knife"
haito uchi ridge-hand strike
hajimae begin
hane springing or bouncing
hane goshi springing hip; throw in judo
hane makikomi springing wrap-around; throw in judo
hangetsu dachi hourglass stance
hanshi honorific title given in recognition of one's character, not just technical ability in a given martial art
hantai reverse; opposite
hantai gatame reverse hold
hara stomach; belly; abdomen
hara gatame armlock applied via the stomach in judo
harai (barai) sweep; sweeping
harai goshi sweeping hip; throw in judo
harai tsurikomi ashi lifting pulling foot sweep; throw in judo
hasami (basami) scissors; pincers of a crab
heisoku dachi attention stance
hidari left (side)
hiji elbow; often used synonymously with empi in Japanese martial arts
hiragana cursive phonetic script used for writing Japanese in combination with kanji
hishigi crush; break; sprain
hittsui incorrect spelling of shittsui
hiza knee
hiza geri knee kick
hiza guruma knee wheel; throw in judo
ho direction; side; way; e.g., shiho
hon counter for long cylindrical objects; e.g., gohon
hombu headquarters; also spelled honbu
honbu alternative spelling of hombu


ichi one (see numerals)
ikkyu first class (see belt ranks)
ippon one long cylindrical object; one full point in a judo contest
ippon ken one-knuckle fist
ippon kumite one-step sparring
ippon seoi one-armed shoulder; throw in judo
irimi waza entering techniques


ji character; letter; word; handwriting; e.g., kanji
jigo-tai defensive posture
jime spelling of shime when following another word
jitsu technique; art; e.g. jujitsu, bujitsu; should technically be spelled jutsu3
jiyu freedom; liberty
jiyu kumite free sparring
jo short staff
jodan upper; shoulder-level or above
jodan juji uke high X-block
jojitsu short staff techniques
joseke upper seat
ju 1. ten (see numerals)
2. gentle; soft; pliant; synonymous with yawara
judan tenth degree; tenth degree black belt (see belt ranks)
judo sport martial art featuring throwing; founded by Jigoro Kano in the late 19th and early 20th centuries; literally, "gentle way"
judoka practitioner of judo
juji cross; literally, "the kanji ju" (whose shape is that of a cross)
juji gatame cross lock
jujitsu self-defense martial art based on grappling and throwing; literally, "gentle technique"
jujitsuka practitioner of jujitsu
juji uke x-block; literally, "cross block"
jutsu alternative (and technically correct3) spelling of jitsu


kaeshi (gaeshi) counter; reversal; return; answer
kagi hook
kagi zuki hook punch
kakato heel
kakato geri heel kick
kake (gake) hooking or clipping action
kakiwake pushing one's way through
kakiwake uke pushing through block
kakuto crane head
kakuto uke bent wrist block; literally, "crane head block"
kama sickle, used in pairs in Okinawan karate
kamae posture with attitude and intention. Uses & history
kami 1. god; spirit; divine
2. upper body; top
kami shiho gatame upper four-direction hold
kan China
kana the Japanese phoenetic alphabets, i.e., hiragana and katakana
kani crab
kani sute crab sacrifice; another name for kani basami
kani basami crab scissors; flying scissors throw of judo which is sometimes also called kani sute
kanji Japanese system of writing utilizing characters from Chinese writing; a single character in this system; literally, "the character kan"
Kano, Jigoro founder of judo
kansetsu knuckle or joint
kansetsu waza joint-locking techniques in judo
kara 1. empty; emptiness
2. China; literally, "T'ang", as in the T'ang dynasty of China
karami (garami) entanglement; entwined
karate martial art emphasizing striking; literally, "empty hand" or "Chinese hand" (see kara)
kata 1. stylized form; pre-arranged techniques used to practice many martial arts
2. shoulder; e.g., kata guruma
3. one-sided; one (of two); e.g., kataha jime
kata gatame shoulder hold
kata guruma shoulder wheel; throw in judo
kata juji jime half cross choke
kataha single edge; single wing
kataha jime single wing choke
katakana angular phonetic script used mainly for writing foreign words in Japanese
katame (gatame) hardening; fortifying; tightening; used in judo to mean grappling or a hold or lock
katame waza grappling techniques of judo; often used interchangeably with ne waza4
katana long sword of the daisho; the primary sword of the samurai worn tucked into the belt with its curved blade facing upward; successor of the tachi; synonymous with to
katate one hand; single hand
katate dori one hand pull
katsu revival techniques
keage upwards kick
kekomi thrusting kick
kempo (kenpo) fist way; Japanese word for (and hence synonymous with) chuan fa
ken 1. fist; e.g., kenpo
2. any generic straight-bladed sword; e.g., kendo
kendo modern Japanese sport martial art of fencing; literally, "way of the sword"; descendant of kenjitsu
kenjitsu combat swordfighting practiced by the bushi; literally, "art of the sword"; predecessor of kendo
kenpo alternative spelling of kempo
keri (geri) kick
keri waza kicking techniques
kesa scarf; in particular, the scarf of a Buddhist monk
kesa gatame scarf hold
ki inner energy; spirit
kiai loud shout or yell which focuses one's ki when striking hard1; literally, "harmonized inner energy"
kiba horse-riding
kiba dachi horse stance; literally, "horse-riding stance"
kime focus
kiotsuke to command someone to pay attention
ko 1. minor; compare to o; e.g., kosoto gari
2. old; ancient; e.g., koryu
3. behind; back; backwards; e.g., kokutsu
Kodokan headquarters of judo in Japan; iterally, "school for studying the way"; also used when referring to judo, as in Kodokan Judo.
koko uchi tiger mouth strike
Kokua To cooperate; to help one-another
kokutsu backward leaning
kokutsu dachi back stance; literally, "backward leaning stance"
komi to be inserted, crowded, or mixed
koryu traditional schools of Japanese martial arts; literally, "ancient or old stream"
koshi (goshi) 1. hip; waist; loin
2. ball of the foot
koshi guruma hip wheel; throw in judo
koshi jime hip choke
koshi waza hip techniques
kosoto gake minor outer clip; throw in judo
kosoto gari minor outer reap; throw in judo
kouchi gari minor inner reap; throw in judo
ku nine (see numerals)
kubi neck
kuchiki a decayed/dead tree
kuchiki taoshi to fell or knock down a decayed/dead tree; throw in judo
kudan ninth degree; ninth degree black belt (see belt ranks)
kumikata methods of holding
kumite sparring
kuruma (guruma) wheel
kusarigama sickle with a rope or chain attached
kutsu lean; stoop; bend
kuzure broken; collapsed
kuzure kesa gatame broken scarf hold
kuzushi unbalancing (in judo, there are eight directions of unbalancing, corresponding to the eight directions of the compass)
kyu class; grade; rank; in Japanese martial arts, used for ranks under black belt (see belt ranks)
kyusho vital or pressure points
kyusho jitsu the art of striking the vital points of the body


ma-ai distance
mae front
mae geri front kick
mae geri keage front snap kick; technically, this is redundant and should be simply mae keage
mae geri kekomi front thrust kick; technically, this is redundant and should be simply mae kekomi
mae keage front snap kick; also referred to as mae geri keage
mae kekomi front thrust kick; also referred to as mae geri kekomi
mae tobi geri front jump kick
maki volume; scroll; reel; roll
maki gaeshi wrapping reversal
makikomi to wrap around, enfold, wind up, or roll up in a whirlpool- or windmill-like movement
makikomi harai wrap-around sweep
makiwara punching board
matae stop
mawashi turning; rotating
mawashi geri roundhouse kick
mawashi zuki roundhouse punch
mi 1. the body; one's self; e.g., sutemi
2. eyebrow
migi right (side)
mikazuki crescent moon; new moon; literally, "three day moon"
mikazuki geri crescent kick
mikazuki geri uke crescent kick block
moro pair; several
morote two hands; both hands
morote seoi nage two-handed shoulder throw; throw in judo
morote zuki two-handed punch
morote uke two-handed block
moro yubi tori two-finger pull
mudansha non-black belt holder
mune chest
mune gatame chest hold
mushin mind of no mind; state of being without thought


nagashi uke flowing block; parry
nage throw
nage waza throwing techniques in judo
nage no kata formalized throws
nagimaki halberd-like weapon similar to the naginata but designed for mounted use
naginata halberd-like weapon used by the samurai in medieval Japan
naginata jutsu art of the naginata
nami juji jime normal cross choke
nana seven (see numerals)
nanadan seventh degree; seventh degree black belt; also called shichidan (see belt ranks)
ne ground; root; base
ne waza ground techniques or matwork in judo; often used interchangeably with katame waza4
neko cat
neko ashi dachi cat stance; literally, "cat-leg stance"
ni two (see numerals)
nidan second degree; second degree black belt (see belt ranks)
nidan geri two step or double jump kick
nihon nukite zuki two finger spear-hand thrust
nikyu second class (see belt ranks)
no archaic possesive particle; e.g., nage no kata
nuki draw; pull out
nukite spear-hand; literally, "(sword) drawing hand"
nukite zuki spear-hand thrust
nunchaku flail-like weapon of two rods joined by rope or chain


o major; compare to ko; e.g., ogoshi
obi belt
ogoshi major hip; throw in judo
oguruma major wheel; throw in judo
outen barrel roll; turning sideways
outen gatame barrel roll hold
oi lunge; chase; pursue
oi zuki lunging punch (same-side hand and leg)
okuri chasing; sliding
okuri ashi barai sliding foot sweep; throw in judo
okuri eri jime sliding collar choke
osae pressure
osae komi pressing; holding-down; pinning; immobilizing
osae komi waza pinning techniques of judo
osoto gari major outer reap; throw in judo
osoto guruma major outer wheel; throw in judo
otoshi drop
ouchi gari major inner reap; throw in judo


randori free practice or sparring in judo
rei bow
rokkyu sixth class (see belt ranks); also spelled rokyu or rokukyu
roku six (see numerals)
rokudan sixth degree; sixth degree black belt (see belt ranks)
rokukyu alternative spelling of rokkyu
rokyu alternative spelling of rokkyu
romaji romanization of Japanese kanji
ryu a style of school in Japanese martial arts; literally, "stream"
Ryukyu the Ryukyu islands, the southernmost island group of Japan; includes Okinawa


sai three-pronged metal weapon
saka alternative pronunciation of the kanji which is also read gyaku (first definition)
saka nuki reverse pull-out
sakotsu collarbone
sakotsu shuto collarbone knife-hand
sakotsu shuto uchi collarbone knife-hand strike
samurai warrior class of medieval Japan; literally, "one who serves"; synonymous with bushi2
san three (see numerals)
sanchin dachi hourglass stance (derived from Sanchin kata)
sandan third degree; third degree black belt (see belt ranks)
sankyu third class (see belt ranks)
sasae propping; supporting
sasae tsurikomi ashi propping lifting pulling foot; throw in judo
Seifukujitsu massage in the tradition of Prof. Henry Okazaki
seiza traditional Japanese sitting position (on knees)
sempai senior
sensei teacher
seoi shoulder
seoi goshi shoulder hip
shi2 1. four (see numerals)
2. death
3. teacher; master; expert; mentor; e.g., shihan
shiai contest
shichi2 seven (see numerals)
shichidan seventh degree; seventh degree black belt; also called nanadan (see belt ranks)
shihan master or senior instructor
shiho every direction; literally, "four directions"
shiho nage four-direction throw; throw in aikido
shime (jime) choke; strangle
shime waza choking or strangling techniques of judo
shittsui knee-hammer
shittsui geri knee-hammer kick
shizen-tai natural posture
shodan beginning degree or step; in Japanese martial arts, used as the rank of 1st degree black belt (see belt ranks)
shotei palm-heel; literally, "bottom of hand"; same as teisho
shotei uchi palm-heel strike; same as teisho uchi
shotei uke palm-heel block; same as teisho uke
shu hand; e.g., shuto uchi
shuto knife-hand (little-finger side of palm); literally, "hand knife"
shuto uchi knife-hand strike; karate chop
shuto uke knife-hand block
sode sleeve
sode tsurikomi goshi sleeve lifting pulling hip; throw in judo
soke head of family; in Japanese martial arts, the headmaster of a martial arts system
soku alternative pronunciation of the kanji which is also read ashi; e.g., haisoku
soto outside; outer
soto age uke outer upper block
soto makikomi outer wrap-around; throw in judo
soto mikazuki geri outer crescent kick
soto shuto uke outside knife-hand block
soto ude uke outside forearm block
sukui to scoop up
sukui nage scooping throw; throw in judo
sumi corner
sumi gaeshi corner reversal; throw in judo
sumi otoshi corner drop; throw in judo
sute sacrifice
sutemi sacrificing one's self
sutemi waza self-sacrificing techniques


tachi (dachi) 1. stance; standing
2. curved sword worn hung from the belt with the blade down; predecessor of the katana
tachi waza standing techniques (techniques done from the standing position)
tai the body
tai otoshi body drop; throw in judo
tama ball; sphere
tameshiwari breaking demonstration
tanden point just below the navel
tani valley
tani otoshi valley drop; throw in judo
tanto knife
taoshi to fell or knock down
tatami a rice straw mat commonly used in traditional Japanese homes to soften the hard wooden floors; also used in some Japanese martial arts to provide a relatively soft surface to take hard falls
tate vertical
tate zuki boxer's jab; literally, "vertical punch"
tatsu 1. dragon
2. standing; rising up
tatsumaki tornado; whirlwind; literally, "dragon roll"
tatsumaki jime dragon choke; literally, "dragon roll choke"
tawara straw rice bag; bale
tawara gaeshi rice bag reversal; throw in judo
te hand
te waza hand techniques
tei 1. street; ward; town
2. bottom; e.g., shotei
teiji the letter "T"; literally, "the kanji tei" (whose shape is that of the roman letter "T")
teiji dachi T-stance
teisho same as shotei
teisho uchi
same as shotei uchi
teisho uke same as shotei uke
tekubi wrist; literally, "neck of the hand"
tekubi tori wrist pull
tensho rolling hand; fluid hand
tettsui iron hammer
tettsui uchi hammer-fist strike; literally, "iron hammer strike"
to alternative pronunciation of the kanji which is also read katana; e.g., haito
tomoe comma-like design or shape
tomoe nage circular throw; literally, "comma-like throw"; throw in judo
tonfa wooden rod with handle at right angle, used in pairs
tora tiger
tora nage tiger throw
tori (dori) pull; grab; grasp; take; take away; in Japanese martial arts, the one who performs or demonstrates ("takes") a technique; compare to uke
tsuki (zuki) 1. thrust; punch; e.g., kagi zuki
2. moon; month; e.g., mikazuki
tsuki waza thrusting techniques
tsukuri stepping into the throw
tsuri fishing; to lift up (as when hooking a fish)
tsuri goshi lifting hip; throw in judo
tsurikomi lifting and pulling up in a circular motion (as when hooking a fish); taking in
tsurikomi goshi lifting pulling hip; throw in judo


uchi 1. inner; inside; e.g., ouchi gari
2. strike; e.g., shotei uchi
uchi makikomi inner wrap-around; throw in judo
uchi mata inner thigh; throw in judo
uchi waza striking techniques
uchi deshi special disciple; literally, "inner student"
uchi komi repeated practice of throwing techniques
ude arm or forearm
ude garami forearm entanglement
ude gatame forearm lock
ude tori forearm pull
ude uke forearm block
Ueshiba, Morihei founder of aikido
uke receiving; in Japanese martial arts, the one who "receives" a technique; also in Japanese martial arts, a block (to "receive" a strike); compare to tori
ukemi breakfalling; literally, "receiving with the body"
ukemi waza breakfalling techniques
uki floating
uki goshi floating hip; throw in judo
uki otoshi floating drop; throw in judo
uki waza floating throw; throw in judo
ura reverse side; back; rear
ura nage back throw; suplex; throw in judo
ura zuki reverse side punch
uraken back of the fist
uraken uchi back fist strike
ushiro back; behind; rear
ushiro geri back kick
ushiro goshi back hip; throw in judo
utsuri shift; switch; transition; change
utsuri goshi switching hip; throw in judo


wakare separation
wakizashi shorter sword of the daisho
waza technique


yama mountain
yama bushi mountain warriors
yama zuki U-punch; literally, "mountain punch"
yari spear
yawara soft; gentle; pliant; synonymous with second definition of ju
yoi ready
yoko side
yoko gake side clip; throw in judo
yoko geri side kick
yoko geri keage side snap kick; technically, this is redundant and should be simply yoko keage
yoko geri kekomi side thrust kick; technically, this is redundant and should be simply yoko kekomi
yoko guruma side wheel; throw in judo
yoko haitto side ridge-hand
yoko haitto uchi side ridge-hand strike
yoko keage side snap kick; also referred to as yoko geri keage
yoko kekomi side thrust kick; also referred to as yoko geri kekomi
yoko otoshi side drop; throw in judo
yoko shiho gatame side four-direction hold
yoko shuto side knife-hand
yoko shuto uchi side knife-hand strike
yoko tobi geri side jump kick
yoko wakare side separation; throw in judo
yon four (see numerals)
yondan fourth degree; fourth degree black belt (see belt ranks)
yonkyu fourth class (see belt ranks)
yubi finger
yubi tori finger pull
yudansha one who is a black belt


zen 1. Japanese sect of Buddhism which places heavy emphasis on meditation and which significantly influenced the Japanese martial arts
2. in front; before; forwards; e.g., zenkutsu
zenkutsu forward leaning
zenkutsu dachi front stance; literally, "forward leaning stance"
zuki spelling of tsuki when following another word


1 ichi
2 ni
3 san
4 yon, shi5
5 go
6 roku
7 nana, shichi5
8 hachi
9 ku
10 ju
11 ju-ichi
12 ju-ni
13 ju-san
14 ju-yon, ju-shi5
15 ju-go
16 ju-roku
17 ju-nana, ju-shichi5
18 ju-hachi
19 ju-ku
20 ni-ju
21 ni-ju-ichi
30 san-ju
40 yon-ju, shi-ju5
50 go-ju
100 hyaku

Belt ranks (lowest to highest)

kyu6 - Colored Belts
rokkyu 6th kyu (White Belt)
gokyu 5th kyu (Blue Belt)
yonkyu 4th kyu (Green Belt)
sankyu 3rd kyu (Brown Belt)
nikyu 2nd kyu (Brown Belt)
ikkyu 1st kyu (Brown Belt)

dan - Black Belt
shodan 1st dan
nidan 2nd dan
sandan 3rd dan
yondan 4th dan
godan 5th dan
rokudan 6th dan
shichidan, nanadan 7th dan
hachidan 8th dan
kudan 9th dan
judan 10th dan


1 Aiki and kiai are reverse arrangments of the same two kanji, ki and ai. Therefore, it is not unexpected that they should have similar meanings. In fact, both aiki and kiai can be considered different manifestations of the same concept--the former a mental or static manifestation and the latter a vocal or dynamic manifestation. Needless to say, these definitions are intended only to be guidelines as they are very open to interpretation.

2 Some experts in Japanese medieval history differentiate between bushi and samurai, considering the latter to be a subset of the former. However, this is not clear and invovles a detailed understanding of Japanese history and culture. Thus, most consider the two words to be synonymous.

3 Technically, jitsu should be spelled jutsu according to the most recent (post-World War II) standards for converting kanji into romaji. The reasons for the variations in its spelling are due to the fact that when the word was first used in the West by Japanese immigrants in the late 19th and early 20th centuries, there was no standard for romaji. Further, even if there was, those who heard Japanese usually had no understanding of the Japanese language and were not aware of any standard and simply tried to transliterate what they heard the best they could. Thus, many modern Japanese jujitsu clubs which were established in the West in the 20th century, have inherited a name for their art that is technically incorrect. However, since the usage of jitsu is so widespread, it is usually accepted as legitimate and actually serves to identify modern styles of jujitsu from more traditional styles. Hence, the Stanford Jujitsu Club has chosen to retain the spelling jitsu while recognizing it is technically incorrect.

4 In the traditional judo curriculum, katame waza consists of three sub-categories: joint-locking techniques (kansetsu waza), strangling/choking techniques (shime waza), and pinning techniques (osae komi waza). Except for the pinning techniques (which are by definition done on the ground), the other two waza can be done either on the ground or standing. Ne waza (ground techniques), however, refers solely to techniques performed on the ground. Hence, some katame waza (e.g., an armbar from the standing position) are not ne waza and katame waza and ne waza should technically be considered distinct. However, since most katame waza are in fact done from the ground, it has become acceptable to use katame waza and ne waza interchangeably.

5 The Japanese word shi also translates as "death". Hence both shi and shichi (a combination of shi and chi) and all numbers which use them are sometimes avoided for superstitious reasons. However, there is no steadfast rule and both spellings can usually be used. Check out Wikipedia's entry on Japanese numerals to see this more clearly (and obtain more info on Japanese numerals).

6 The original kyu/dan belt ranking system created by Jigoro Kano, founder of judo, in the early 20th century only had 6 kyu ranks. Some systems use more.