The Collaborative International Dictionary of English v.0.48:
Buoy \Buoy\ (bwoi or boi; 277), 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
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
Nut buoy 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.