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.
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.]
(click for a larger image)valve
top: closed check valve
bottom: open check valve
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
The American Heritage Dictionary Blog
Check out our blog, updated regularly, for new words and revised definitions, interesting images from the 5th edition, discussions of usage, and more.
American Heritage Dictionary Products
The American Heritage Dictionary, 5th Edition
The American Heritage Dictionary of Idioms
The American Heritage Roget's Thesaurus
Curious George's Dictionary
The American Heritage Children's Dictionary
The American Heritage Dictionary of Indo-European Roots
The American Heritage Student Grammar Dictionary
The American Heritage Desk Dictionary + Thesaurus
The American Heritage Science Dictionary
The American Heritage Dictionary of Business Terms
The American Heritage Student Dictionary
The American Heritage Essential Student Thesaurus