noun
light blue samurai costume worn for ritual suicide
Historical term for a specific light blue kamishimo (裃) ensemble traditionally donned by samurai when performing seppuku. Rarely encountered outside historical or literary contexts.
時代劇で、切腹の場面になると水上下を着た武士が現れる。
In period dramas, a samurai wearing a light blue kamishimo appears when it's time for seppuku.
裃 is the general term for the samurai formal attire consisting of kataginu and hakama. 水上下 specifically refers to the light blue variant associated with seppuku.
Compound of 水 (mizu, 'water') and 上下 (kamishimo, 'samurai formal attire'), referring to the light blue color reminiscent of water. The exact historical origin of the color association is uncertain.