An antechamber is a small room you pass through before you reach the main room — often a waiting room just outside a more important space. Palaces, courts, and grand offices had them: you sit or stand there until you are called in. Anteroom is the same idea and is the more everyday English word; antechamber feels a little older and more formal, the kind of word you meet in history, palaces, and novels. People also stretch it: an antechamber to something can mean a place or stage that is only a step on the way to something bigger, not a room at all. It is not a bedroom, and it is not a secret hidden chamber. The French source looks like anti-, but that piece is the same ‘before’ idea as ante-, not ‘against’.

前廳；接待室（進正廳或大人物房間之前的小間）