Definitions of buoy:

• noun:   bright-colored; a float attached by rope to the seabed to mark channels in a harbor or underwater hazards
• verb:   mark with a buoy
• verb:   keep afloat

  Example: "The life vest buoyed him up"

• verb:   float on the surface of water
• name:  A surname (very rare: popularity rank in the U.S.: #38477)