The Collaborative International Dictionary of English v.0.48:

Valve \Valve\, n. [L. valva the leaf, fold, or valve of a door:
   cf. F. valve.]
   [1913 Webster]
   1. A door; especially, one of a pair of folding doors, or one
      of the leaves of such a door.
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            Swift through the valves the visionary fair
            Repassed.                             --Pope.
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            Heavily closed, . . . the valves of the barn doors.
                                                  --Longfellow.
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   2. A lid, plug, or cover, applied to an aperture so that by
      its movement, as by swinging, lifting and falling,
      sliding, turning, or the like, it will open or close the
      aperture to permit or prevent passage, as of a fluid.
      [1913 Webster]

   Note: A valve may act automatically so as to be opened by the
         effort of a fluid to pass in one direction, and closed
         by the effort to pass in the other direction, as a
         clack valve; or it may be opened or closed by hand or
         by mechanism, as a screw valve, or a slide valve.
         [1913 Webster]

   3. (Anat.) One or more membranous partitions, flaps, or
      folds, which permit the passage of the contents of a
      vessel or cavity in one direction, but stop or retard the
      flow in the opposite direction; as, the ileocolic, mitral,
      and semilunar valves.
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   4. (Bot.)
      (a) One of the pieces into which a capsule naturally
          separates when it bursts.
      (b) One of the two similar portions of the shell of a
          diatom.
      (c) A small portion of certain anthers, which opens like a
          trapdoor to allow the pollen to escape, as in the
          barberry.
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   5. (Zool.) One of the pieces or divisions of bivalve or
      multivalve shells.
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   Air valve, Ball valve, Check valve, etc. See under
      Air. Ball, Check, etc.

   Double-beat valve, a kind of balance valve usually
      consisting of a movable, open-ended, turban-shaped shell
      provided with two faces of nearly equal diameters, one
      above another, which rest upon two corresponding seats
      when the valve is closed.

   Equilibrium valve.
      (a) A balance valve. See under Balance.
      (b) A valve for permitting air, steam, water, etc., to
          pass into or out of a chamber so as to establish or
          maintain equal pressure within and without.

   Valve chest (Mach.), a chamber in which a valve works;
      especially (Steam Engine), the steam chest; -- called in
      England valve box, and valve casing. See Steam
      chest, under Steam.

   Valve face (Mach.), that part of the surface of a valve
      which comes in contact with the valve seat.

   Valve gear, or Valve motion (Steam Engine), the system of
      parts by which motion is given to the valve or valves for
      the distribution of steam in the cylinder. For an
      illustration of one form of valve gear, see Link motion.


   Valve seat. (Mach.)
      (a) The fixed surface on which a valve rests or against
          which it presses.
      (b) A part or piece on which such a surface is formed.

   Valve stem (Mach.), a rod attached to a valve, for moving
      it.

   Valve yoke (Mach.), a strap embracing a slide valve and
      connecting it to the valve stem.
      [1913 Webster]