Source : Webster's Revised Unabridged Dictionary (1913)

Valve \Valve\, n. [L. valva the leaf, fold, or valve of a door:
   cf. F. valve.]
   1. A door; especially, one of a pair of folding doors, or one
      of the leaves of such a door.

            Swift through the valves the visionary fair
            Repassed.                             --Pope.

            Heavily closed, . . . the valves of the barn doors.
                                                  --Longfellow.

   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.

   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.

   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.

   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.

   5. (Zo["o]l.) One of the pieces or divisions of bivalve or
      multivalve shells.

   {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.

Ball \Ball\ (b[add]l), n. [OE. bal, balle; akin to OHG. balla,
   palla, G. ball, Icel. b["o]llr, ball; cf. F. balle. Cf. 1st
   {Bale}, n., {Pallmall}.]
   1. Any round or roundish body or mass; a sphere or globe; as,
      a ball of twine; a ball of snow.

   2. A spherical body of any substance or size used to play
      with, as by throwing, knocking, kicking, etc.

   3. A general name for games in which a ball is thrown,
      kicked, or knocked. See {Baseball}, and {Football}.

   4. Any solid spherical, cylindrical, or conical projectile of
      lead or iron, to be discharged from a firearm; as, a
      cannon ball; a rifle ball; -- often used collectively; as,
      powder and ball. Spherical balls for the smaller firearms
      are commonly called {bullets}.

   5. (Pyrotechnics & Mil.) A flaming, roundish body shot into
      the air; a case filled with combustibles intended to burst
      and give light or set fire, or to produce smoke or stench;
      as, a fire ball; a stink ball.

   6. (Print.) A leather-covered cushion, fastened to a handle
      called a ballstock; -- formerly used by printers for
      inking the form, but now superseded by the roller.

   7. A roundish protuberant portion of some part of the body;
      as, the ball of the thumb; the ball of the foot.

   8. (Far.) A large pill, a form in which medicine is commonly
      given to horses; a bolus. --White.

   9. The globe or earth. --Pope.

            Move round the dark terrestrial ball. --Addison.

   {Ball and socket joint}, a joint in which a ball moves within
      a socket, so as to admit of motion in every direction
      within certain limits.

   {Ball bearings}, a mechanical device for lessening the
      friction of axle bearings by means of small loose metal
      balls.

   {Ball cartridge}, a cartridge containing a ball, as
      distinguished from a blank cartridge, containing only
      powder.

   {Ball cock}, a faucet or valve which is opened or closed by
      the fall or rise of a ball floating in water at the end of
      a lever.

   {Ball gudgeon}, a pivot of a spherical form, which permits
      lateral deflection of the arbor or shaft, while retaining
      the pivot in its socket. --Knight.

   {Ball lever}, the lever used in a ball cock.

   {Ball of the eye}, the eye itself, as distinguished from its
      lids and socket; -- formerly, the pupil of the eye.

   {Ball valve} (Mach.), a contrivance by which a ball, placed
      in a circular cup with a hole in its bottom, operates as a
      valve.

   {Ball vein} (Mining), a sort of iron ore, found in loose
      masses of a globular form, containing sparkling particles.
      

   {Three balls}, or {Three golden balls}, a pawnbroker's sign
      or shop.

   Syn: See {Globe}.

Source : WordNet®

ball valve
     n : any valve that checks flow by the seating of a ball