\Buoy"an*cy\, n.; pl. {Buoyancies}.
1. The property of floating on the surface of a liquid, or in
   a fluid, as in the atmosphere; specific lightness, which
   is inversely as the weight compared with that of an equal
   volume of water.
2. (Physics) The upward pressure exerted upon a floating body
   by a fluid, which is equal to the weight of the body;
   hence, also, the weight of a floating body, as measured by
   the volume of fluid displaced.
         Such are buoyancies or displacements of the
         different classes of her majesty's ships. --Eng.
                                               Cyc.
3. Cheerfulness; vivacity; liveliness; sprightliness; -- the
   opposite of {heaviness}; as, buoyancy of spirits.