Ninja is an on'yomi (Early Middle Chinese-influenced) reading of the two kanji '敹?????. In the native kun'yomi kanji reading, it is pronounced shinobi, a shortened form of the transcription shinobi-no-mono (敹??????. These two systems of pronouncing kanji create words with similar meanings.

The word shinobi appears in the written record as far back as the late 8th century in poems in the Man'y?sh贖. The underlying connotation of shinobi (敹? means 'to steal away', hence its association with stealth and invisibility. Mono (?? means 'a person'. It also relates to the term shinobu, which means to hide.

Historically, the word ninja was not in common use, and a variety of regional colloquialisms evolved to describe what would later be dubbed ninja.