(1):

(v. t.) To keep from sinking in a fluid, as in water or air; to keep afloat; - with up.

(2):

(v. i.) To float; to rise like a buoy.

(3):

(v. t.) To fix buoys to; to mark by a buoy or by buoys; as, to buoy an anchor; to buoy or buoy off a channel.

(4):

(n.) 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.

(5):

(v. t.) To support or sustain; to preserve from sinking into ruin or despondency.