also: どしうち
noun
friendly fire; accidental killing of allies
Refers to accidentally attacking or killing one's own side in battle or conflict. Often used in military or historical contexts.
戦場では同士討ちを避けるために、目印をつけていた。
On the battlefield, they wore markers to avoid friendly fire.
その事故は同士討ちによるものだった。
The incident was due to friendly fire.
noun
internecine strife; infighting among allies
Extended meaning: conflict or struggle within a group that should be united. Can be used metaphorically for political or organizational infighting.
党内の同士討ちが選挙の敗因となった。
Infighting within the party led to the election loss.
同士討ちをしている場合ではない。
This is no time for fighting among ourselves.
内輪もめ refers to internal quarrels or family disputes, often petty, while 同士討ち emphasizes the irony of allies harming each other, with a stronger connotation of betrayal or tragic mistake.
仲間割れ means a split or falling-out among comrades, focusing on the breakdown of relationships, whereas 同士討ち highlights the active conflict or harm between them.
Compound of 同士 (dōshi, 'comrades, fellows') and 討ち/打ち (uchi, 'striking, attacking'). The literal meaning is 'comrade-striking', naturally extended to both accidental friendly fire and deliberate infighting.