出典:Wiktionary
republican + queen. From the United States being a republic, and queens being the martial consort of the leader of a kingdom (a king), where the US had recently became independent from such an entity (Great Britain, under King George); thus terming the consort of the male president a form of queen.
The term First Lady was not used until the 1849 funeral of Dolley Madison, wife of ex-president James Madison (term 1809-1817), by then-President Zachary Taylor, for the wife of a president of the United States.[4][5][6]