ninja

noun, plural nin·ja, nin·jas.

1. (often initial capital letter) 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.
2. a person who is expert or highly skilled in a specified field or activity (often used attributively): marketing ninjas; ninja gamers.

noun plural -ja or -jas

1. (sometimes capital) a person skilled in ninjutsu, a Japanese martial art characterized by stealthy movement and camouflage