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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.
(noun)
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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.
(noun)
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The movable control element of such a device.
(noun)
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Music A device in a brass wind instrument that permits change in pitch by a rapid varying of the air column in a tube.
(noun)
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Biology One of the paired, hinged shells of certain mollusks and of brachiopods.
(noun)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.