aqualung

Trademark.

1. a brand of underwater breathing apparatus for a swimmer or skin-diver, consisting of a cylinder of compressed air that is strapped to the back, a flexible tube connecting the cylinder with the swimmer’s mouth, and an automatic pressure regulator that controls the flow of air into the lungs.

noun

1. breathing apparatus used by divers, etc, consisting of a mouthpiece attached to air cylinders strapped to the back