noun
informal family crest; auxiliary crest
Archaic term for a secondary or informal family crest used in place of the formal one, often in less official settings.
江戸時代には、武士が略式の場で替え紋を用いることがあった。
In the Edo period, samurai sometimes used an informal family crest on casual occasions.
家紋 is the formal, official family crest, while 替え紋 is an informal or substitute version.
Compound of 替え (substitute) and 紋 (crest). The exact historical derivation is uncertain, but the term refers to a secondary crest used in place of the main family crest.