In Japanese history, a is a warrior, trained in martial arts, and specializing in a variety of unorthodox arts of war. The methods used by ninja included assassination, espionage, stealth, camouflage, specialized weapons, and a vast array of martial arts were added after the 20th century.

The exact origins are unknown, but their roles may have included sabotage, espionage, scouting and assassination missions as a way to destabilize and cause social chaos in enemy territory or against an opposing ruler, perhaps in the service of their feudal rulers (daimyo, shogun), or an underground ninja organization waging guerilla warfare.

Etymology

Ninja is the on'yomi reading of the two kanji 忍者 used to write shinobi-no-mono (忍の者), which is the native Japanese word for people who practice ninjutsu (忍術, sometimes erroneously transliterated as ninjitsu). The term shinobi (historically sino₂bi₂ written with the Man'yōgana 志能備), has been traced as far back as the late 8th century to a poemTakagi, Man'yōshū poem #3940; page 191Satake, Man'yōshū poem #3940; page 108 to Ōtomo no Yakamochi. The underlying connotation of shinobi (忍) means "to steal away" and—by extension—"to forbear", hence its association with stealth and invisibility. Mono (者, likewise pronounced sha or ja) means a "person."

The word ninja became popular in the post-World War II culture. The nin of ninjutsu is the same as that in ninja, whereas jutsu (術) means skill or art, so ninjutsu means "the skill of going unperceived" or "the art of stealth"; hence, ninja and shinobi-no-mono (as well as shinobi) may be translated as "one skilled in the art of stealth." Similarly, the pre-war word ninjutsu-zukai means "one who uses the art of remaining unperceived."

Other terms which may be used include oniwaban (お庭番 "one in the garden"), suppa, rappa, mitsumono, kusa (草 grass) and Iga-mono ("one from Iga").

In English, the plural of ninja can be either unchanged as ninja, reflecting the Japanese language's lack of grammatical number, or the regular English plural ninjas.

Historical period of origin