noun
just cause; good reason; pretext; justification
Refers to a morally or publicly acceptable reason for an action, often used in political, military, or organizational contexts. Can carry a nuance of a pretext or excuse when the stated reason is not the real motive.
戦争を始めるには大義名分が必要だ。
A just cause is necessary to start a war.
He cited the economic crisis as justification for the reforms.
noun
duty to one's country or sovereign
A more traditional, somewhat archaic sense referring to a moral obligation to serve one's country or ruler. Rare in modern everyday speech but still understood in historical or formal contexts.
武士にとって主君への大義名分は絶対だった。
For samurai, duty to their lord was absolute.