Pronunciation: (nin'ju), [key]
—pl. -ja, -jas. (often cap.)
a member of a feudal Japanese society of mercenary agents, highly trained in martial arts and stealth (ninjutsu), who were hired for covert purposes ranging from espionage to sabotage and assassination.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.