Definition of: buoy

(boi, b′ē) noun
1. Naut. A float moored on a dangerous rock or shoal or at the edge of a channel, as a guide to navigators. Many are named according to shape or function: can buoy (cylindrical); nun buoy (conical); spar buoy (a spar anchored at one end); bell buoy, whistling buoy (buoys devised to sound with the motion of the waves: used to mark dangerous shoals or harbor entrances, respectively).
2. Any device or object for keeping a person in the water afloat: also called lifebuoy. Compare BREECHES BUOY.
—v.t.
1. To keep from sinking in a liquid; keep afloat.
2. To sustain the courage or heart of; encourage: usually with up.
3. Naut. To mark, as a channel, with buoys. [<MDu. boeie]
TYPES OF BUOYS
a. Nun buoy.
b. Can buoy.
c. Spar buoy.
d. Bell buoy.
e. Whistling buoy.
f. Gas–lighted buoy.