n.
     - a device for controlling the passage of fluid through a pipe or duct, especially an automatic device which allows movement in one direction only.
 - a cylindrical mechanism to vary the effective length of the tube in a brass musical instrument.
 - Anatomy  & Zoology  a membranous fold in an organ or vessel which allows blood or other fluid to flow in one direction.
 - Zoology  each of the halves of the hinged shell of a bivalve mollusc or brachiopod.
 - Botany  each of the halves or sections into which a dry fruit dehisces.
 
 
  Derivative
  
    - valved adj.
  - valveless adj.
 
   
  Etymology
  ME (denoting a leaf of a folding or double door): from L. valva.