Kunoichi indicates female ninja in the jargon of ninja (professional spies in Japan, highly trained in stealth and secrecy), and the use of females as a trick was called kunoichi no jutsu (art of kunoichi).
くノ一（くのいち）は忍者の隠語で女性のことを指し、仕事のしかけに女性を使うことをくのいちの術と呼んだ。