Kaiken (dagger)

A kaiken (懐剣) is a 20 – long, single or (very rarely) double-edged Japanese knife usually without ornamental fittings housed in a plain but lacquered mount.

Uses
The was once carried by men and women of the samurai class in Japan. It was useful for self-defense in indoor spaces where the long-bladed katana and intermediate-length were inconvenient. Women carried them in their kimono either in a pocket-like space or in the sleeve pouch  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 with her when she moved in with her husband. The was also carried concealed in its  by the lower classes who were not permitted to wear swords, in particular by criminals in the Edo period.

In modern Japan, a is worn as a traditional accessory for the  (referee) in sumo matches for the highest ranks. However, a real blade is not used. No one legally wears or carries a today in Japan, as this is a violation of the Gun and Sword Law. They can be legally transported, however, provided they are carried together with their registration certificate.

Orthography
Due to pronunciation changes over time, the blade's name has shifted from to. The is also referred to as a  or a protection sword/blade (守り刀).