Anteroom is a noun.
An anteroom is a foyer. Please meet me in the anteroom.
i waited in an anteroom
The men were in the anteroom waiting to be called into the office.
An anteroom is a room you enter before you enter the main room. A cloakroom just inside a door is an anteroom. So is the waiting room of an office.
An anteroom is a small waiting area that usually leads to one or more other rooms.
The butler ushered us into an ajoining anteroom and instructed us to wait, while he informed his master of our arrival.
foyer, antechamber, lobby, vestibule, waiting room
The correct spelling is "anteroom" (a small adjoining room or foyer).
entrance hall, lobby, reception area, vestibule, anteroom, antechamber
He's in the wardrobe, next to the anteroom. It was the 3rd room you entered in the game.
William Hervey Woods has written: 'The anteroom and other poems ..'