A kaiken(懐剣?, prior to modern orthographic reform kwaiken (pocket knife); also futokoro-gatana) is an 8-10 inch long, single or double bladed dagger without ornamental fittings housed in a plain mount, formerly carried by men and women of the samurai class in Japan. It was useful for self-defense indoors where the long katana and intermediate wakizashi were inconvenient. Women carried them in their kimono either in a pocket like fold (futukoro) or in the sleeve (tamoto) for self-defense and for ritual suicide by slashing the veins in the left side of the neck. When a samurai woman married, she was expected to carry a kaiken with her when she went to her husband's house to live.
^The complete encyclopedia of arms & weapons: the most comprehensive reference work ever published on arms and armor, Claude Blair, Publisher Bonanza Books, 1986, ISBN 0-517-48776-4, ISBN 978-0-517-48776-1 P.306
^The sword book in Honchō gunkikō and The book of Samé, Kō hi sei gi of Inaba Tsūriō, Authors Hakuseki Arai, Tsūryū Inaba, Publisher C. E. Tuttle, 1963 P.42