<p><strong>Noun:</strong></p><ul><li>Any device for halting or controlling the flow of a liquid, gas, or other material through a passage, pipe, inlet, outlet, etc.</li><li>A hinged lid or other movable part that closes or modifies the passage in such a device.</li><li>Anatomy: A membranous fold or other structure that controls the flow of a fluid, as one that permits blood to flow in one direction only.</li><li>(In musical wind instruments of the trumpet class) A device for changing the length of the air column to alter the pitch of a tone.</li><li>Zoology: One of the two or more separable pieces composing certain shells.</li><li>Either half of the silicified shell of a diatom.</li><li>Botany: One of the segments into which a capsule dehisces.</li><li>A flap or lidlike part of certain anthers.</li><li>Electronics (chiefly British): Vacuum tube.</li><li>Archaic: One of the leaves of a double or folding door.</li></ul><p><strong>Verb:</strong></p><ul><li>(used with object) To provide with a means of controlling the flow of liquid, gas, etc., by inserting a valve.</li></ul>