ninja

The term "ninja" is the on'yomi (Sino-Japanese) reading of the Japanese compound 忍者. Its earlier, synonymous form in Japanese is "shinobi," which is the kun'yomi (native Japanese) reading of the same first character 忍. The concept originates from feudal Japan, where ninja were covert agents and mercenaries specializing in unconventional warfare, espionage, and infiltration. The word entered English in the 20th century, initially through translations of Japanese texts and later popularized globally by martial arts films and comic books. Its meaning has since broadened in informal English to describe anyone who demonstrates exceptional skill or moves with great stealth in any domain.

The word "ninja" is a Japanese loanword. It is a compound of the kanji characters 忍 (nin, meaning "endurance," "stealth," or "perseverance") and 者 (ja or sha, meaning "person"). In its borrowing into English, it is treated as an unsegmentable simplex word.