omotewaza 表技 ( おもてわざ ) - the basic techniques of a ryuuha lit. outer technique

onkenjutsu 穏剣術 ( おんけんじゅつ ) - another term for shurikenjutsu; may refer to using shuriken in the hands

onmitsu 隠密 ( おんみつ ) - spy; detective; someone who secretly observes

onmyoudou 陰陽道 ( おんみょうどう ) - raditional Japanese esoteric cosmology

oodachi 大太刀 ( おおだち ) - sword with a blade length of around 3 shaku

oosode 大袖 ( おおそで ) - armored protection for the upper arms and shoulders

ooyoroi 大鎧 ( おおよろい ) - older style of armor

outen 横転 ( おうてん ) - cartwheel done for ukemi