any device in a pipe or tube that permits a flow in one direction only, or regulates the flow of whatever is in the pipe, by means of a flap, lid, plug, etc. acting to open or block passage
the flap, lid, plug, etc.
Music a device in certain brass instruments, as the trumpet, that opens (or closes) an auxiliary to the main tube, lengthening (or shortening) the air column and lowering (or raising) the pitch
Zool.
each separate part making up the shell of a mollusk, barnacle, etc.
any of the parts forming the sheath of an ovipositor in certain insects
Anatomy A membranous structure in a hollow organ or passage, as in an artery or vein, that folds or closes to prevent the return flow of the body fluid passing through it.
a. Any of various devices that regulate the flow of gases, liquids, or loose materials through piping or through apertures by opening, closing, or obstructing ports or passageways.
b. The movable control element of such a device.
c. Music A device in a brass wind instrument that permits change in pitch by a rapid varying of the air column in a tube.
Biology
a. One of the paired, hinged shells of certain mollusks and of brachiopods.
b. One of the two silicified halves of the cell wall of a diatom.
c. The entire, one-piece shell of a snail and certain other mollusks.
Botany
a. One of the sections into which the wall of a seedpod or other dehiscent fruit splits.
b. A lidlike covering of an anther.
Chiefly British An electron tube or a vacuum tube.