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 Narabini Hyakuin (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.
Female ninja are mentioned in Bansenshukai, a 17th-century Japanese book compiling the knowledge of the clans in the Iga and Kōga regions devoted to the training of ninja. According to this document, the primary function of female ninja was espionage, finding legitimate service positions in the households of enemies, to accumulate knowledge by gaining trust or overhearing conversations. One historically accepted example of this is Mochizuki Chiyome, the 16th century noblewoman with ninja roots who was tasked by the warlord Takeda Shingen with recruiting women to create a secret network of a few hundred female spies.
Kunoichi typically would never resort to combat and rely on seduction if they had the duty to assassinate. They often used small compact weapons to hide in their kimonos. For example, the neko te were "cat claws" that would scratch and would sometimes be dipped in a poison before use. Tessen, folding fans, were also in use as they can be a "weapon hid in plain sight" because tessen were carried around by everyone in the era. Screaming would also allow discomfort to the target and attract attention if a Kunoichi were to get hurt or threatened before running away.