tank top

noun

1. a close-fitting, low-cut top having shoulder straps and often made of lightweight, knitted fabric.

noun

1. a sleeveless upper garment with wide shoulder straps and a low neck, usually worn over a shirt, blouse, or jumper

n.1968, from tank suit “one-piece bathing costume” (1920s), so called because it was worn in a swimming tank (n.), i.e. pool.