noun
Refers to the act of cutting off someone's head, especially as a form of execution in historical contexts.
江戸時代には、打ち首が刑罰の一つだった。
In the Edo period, decapitation was one of the punishments.
Compound of 打ち (uchi, 'striking') + 首 (kubi, 'neck'). The exact historical derivation is uncertain, but the term straightforwardly refers to striking the neck to sever the head.