n. A folded horizontal band used as a decorative top of a strapless dress or swimsuit. Also a fabric bra top of a 2-piece swimsuit.
In the 1920s, bandeau referred to a simply shaped brassiere, usually of a soft fabric and delicate trimmings providing little support or shaping. By the 1950s, it came to refer to a structured outer garment worn around the breast area, following the contours of the body, but still retaining a relatively simple circle or band shape. A bandeau top was usually worn as part of a swimwear or sportswear ensemble and paired with a cropped jacket or bolero.