snorkel

(noun) breathing device consisting of a bent tube fitting into a swimmer's mouth and extending above the surface; allows swimmer to breathe while face down in the water.

(noun) air passage provided by a retractable device containing intake and exhaust pipes; permits a submarine to stay submerged for extended periods of time. Synonyms: schnorkel, schnorchel, snorkel breather, breather.

(verb) dive with a snorkel.