A historical covert agent in feudal Japan trained in ninjutsu. In modern usage, often refers to the pop-culture figure.
See also: 忍術
Ninjas infiltrated enemy territory using ninjutsu.
The main character of that anime is a ninja.
He walked without making a sound, like a ninja.
The children dressed up as ninjas for the party.
He went into the mountains to train as a ninja.
侍 refers to a samurai warrior who openly served a lord, whereas 忍者 refers to a covert agent trained in stealth and espionage.
忍者 are covert agents or spies trained in stealth, distinct from 武士 who were the officially recognized ruling warrior class.
Standard kanji spelling; widely recognized and used in modern contexts.
From 忍 (nin, 'to endure, conceal') + 者 (sha, 'person'). The reading にんじゃ is a regular on'yomi combination.