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n. 1. 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. A device in a brass wind instrument that can be opened or closed to change the pitch by altering the length of the air column in the tube. 2. 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. 3. Biology a. A piece of shell covering or enclosing certain mollusks or other invertebrates, especially the single one of a univalve mollusk or one of the paired hinged ones of a bivalve mollusk or brachiopod. b. One of the two siliceous halves of the cell wall of a diatom. 4. One of the pieces into which a plant part splits at maturity, especially a segment of a fruit capsule or of certain anthers. 5. Chiefly British An electron tube or a vacuum tube. 6. Archaic Either half of a double or folding door. tr.v. valved, valv·ing, valves 1. To provide with a valve. 2. To control by means of a valve. [Middle English, leaf of a door, from Latin valva; see wel-2 in the Appendix of Indo-European roots.] valveless adj.  (click for a larger image) valvetop: closed check valve bottom: open check valve |
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