side curtain noun 1.: a curtain attached or fitted so as to be attached at the side of something (as a vehicle, window, or building) < the side curtains of an automobile > < canvas side curtains for a tent > 2. a.: one of several canvas weather cloths rigged vertically between the deck or the bulwarks and the ridgerope of a ship b.: one of several similar cloths used to close the openings between the hull and the canopy of a small boat