A member of a class of medieval Japanese mercenary agents who were trained in the martial arts and hired for covert operations such as assassination and sabotage.
Any of a class of feudal Japanese warriors highly trained in stealth and employed as spies and assassins.
The definition of ninja is a warrior or assasin trained in the martial art ninjutsu, including the stealth methods of disguise, warfare and weapon skills.
An example of a ninja is Hattori Hanzo of Japan, a samurai who lived from 1542 to 1596, whose descendants published ninjutsu manuals.
Origin of ninja
Japanese nin to endure (from Early Middle Chinese ɲin’) (also the source of Mandarin rěn) sha person (from Middle Chinese tʂia´ pronoun for head of a relative clause) (also the source of Mandarin zhě)