Source : Webster's Revised Unabridged Dictionary (1913)

Buoy \Buoy\, v. i.
   To float; to rise like a buoy. ``Rising merit will buoy up at
   last.'' --Pope.

Buoy \Buoy\, n. [D. boei buoy, fetter, fr. OF. boie, buie,
   chain, fetter, F. bou['e]e a buoy, from L. boia. ``Boiae
   genus vinculorum tam ferreae quam ligneae.'' --Festus. So
   called because chained to its place.] (Naut.)
   A float; esp. a floating object moored to the bottom, to mark
   a channel or to point out the position of something beneath
   the water, as an anchor, shoal, rock, etc.

   {Anchor buoy}, a buoy attached to, or marking the position
      of, an anchor.

   {Bell buoy}, a large buoy on which a bell is mounted, to be
      rung by the motion of the waves.

   {Breeches buoy}. See under {Breeches}.

   {Cable buoy}, an empty cask employed to buoy up the cable in
      rocky anchorage.

   {Can buoy}, a hollow buoy made of sheet or boiler iron,
      usually conical or pear-shaped.

   {Life buoy}, a float intended to support persons who have
      fallen into the water, until a boat can be dispatched to
      save them.

   {Nut} or {Nun buoy}, a buoy large in the middle, and tapering
      nearly to a point at each end.

   {To stream the buoy}, to let the anchor buoy fall by the
      ship's side into the water, before letting go the anchor.
      

   {Whistling buoy}, a buoy fitted with a whistle that is blown
      by the action of the waves.

Buoy \Buoy\, v. t. [imp. & p. p. {Buoyed}; p. pr. & vb. n.
   {Buoying}.]
   1. To keep from sinking in a fluid, as in water or air; to
      keep afloat; -- with up.

   2. To support or sustain; to preserve from sinking into ruin
      or despondency.

            Those old prejudices, which buoy up the ponderous
            mass of his nobility, wealth, and title. --Burke.

   3. To fix buoys to; to mark by a buoy or by buoys; as, to
      buoy an anchor; to buoy or buoy off a channel.

            Not one rock near the surface was discovered which
            was not buoyed by this floating weed. --Darwin.

Source : WordNet®

buoy
     n : bright-colored; a float attached by rope to the seabed to
         mark channels in a harbor or underwater hazards

buoy
     v 1: float on the surface of water
     2: keep afloat; "The life vest buoyed him up" [syn: {buoy up}]
     3: mark with a buoy