Kunoichi (くノ一) is the term for a female ninja or practitioner of ninjutsu (ninpo).  The term is thought to derive from the names of characters that resemble the three strokes in the kanji character for woman (女 onna); said in the order they are written: ku (く) - no (ノ) - ichi (一). Early literary quotes include Enshū Senkuzuke Narabi Nihyaku In (遠舟千句附并百韵) (1680) as well as Maekuzukeshū (前句付集) (1716), which specifically associates the word with the kanji 女 supporting the etymology. The "くノ一" writing requires the use of one character from each Japanese system of writing — first hiragana, then katakana, then kanji. While hiragana and kanji can exist in the same word, katakana generally cannot appear in conjunction with the others. There are exceptions to this, e.g. "ゴミ箱", "消しゴム".

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A popular etymology would derive the term from 九能一 (能 "nō" : talent) with Japanese numbers "ku" (九) for "nine", the particle "no" (の) for "and" and "ichi" (一) for "one", literally translated to "nine and one". The meaning for this name is derived from the number of orifices on a female body. A male has nine, a female has one more (vaginal opening) and possesses the skills to make use of this orifice as well. Another theory asserts that the term is apocryphal and coined in the writings of Ninpōchō novelist Futaro Yamada.

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The eighth volume of the Bansenshukai written in 1676 by Fujibayashi Yasutake, describes the art of Kunoichi-no-jutsu (くノ一の術, Ninjutsu of female ninja). This can be translated as "a technique to use a female" and was employed for infiltration purposes. The Bansenshukai compiles the knowledge of various ninja clans from the Iga and Koka regions dedicated to the formation and understanding of ninjutsu. According to this document, the main function of the Kunoichi was espionage, finding functions in enemy residence, to gather knowledge, gain trust and or listen to conversations.

 

The Bansenshukai (萬川集海) translates as “All Rivers Merge into the Sea”, meaning that the Bansenshukai is the ultimate collection of all Iga & Koka Ninjutsu and is regarded by scholars as the Bible of Ninjutsu