air passage provided by a retractable device containing intake and exhaust pipes; permits a submarine to stay submerged for extended periods of time
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
perceptible by the senses or intellect; "things happen in the earth and sky with no discernible cause"; "the newspaper reports no discernible progress in the negotiations"; "the skyline is easily discernible even at a distance of several miles"
capable of being seen or noticed; "a discernible change in attitude"; "a clearly evident erasure in the manuscript"; "an observable change in behavior"
capable of being perceived clearly; "an essay with a meaning that was not always discernible"
marked by or capable of arousing controversy; "the issue of the death penalty is highly controversial"; "Rushdie's controversial book"; "a controversial decision on affirmative action"