Webster's English Dictionary

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valve

valve \'valv\ \'valvd\ n [L valva; akin to L volvere to roll - more at 
   VOLUBLE] [NL valva, fr. L] [NL valva, fr. L] [NL valva, fr. L] often attrib 
    archaic  1: a leaf of a folding or double door  2: a structure esp. in a 
   vein or lymphatic that closes temporarily a passag e or orifice or permits 
   movement of fluid in one direction only 3a: any of numerous mechanical 
   devices by which the flow of liquid, gas (as  air), or loose material in 
   bulk may be started, stopped, or regulated by a movable part that opens, 
   shuts, or partially obstructs one or more ports or passageways; also : the 
   movable part of such a device 3b: a device in a brass wind instrument for 
   quickly varying the tube length  in order to change the fundamental tone by 
   some definite interval chiefly Brit  3c: ELECTRON TUBE  4: one of the 
   distinct and usu. movably articulated pieces of which the she ll of 
   lamellibranch mollusks, brachiopods, barnacles, and some other 
   shell-bearing animals consists 5a: one of the segments or pieces into which 
   a dehiscing capsule or legume  separates 5b: the portion of various anthers 
   (as of the barberry) resembling a lid  5c: one of the two encasing 
   membranes of a diatom  - valved aj