from
The Collaborative International Dictionary of English v.0.48
Buoyancy \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.
[1913 Webster]
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.
[1913 Webster]
Such are buoyancies or displacements of the
different classes of her majesty's ships. --Eng.
Cyc.
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3. Cheerfulness; vivacity; liveliness; sprightliness; -- the
opposite of {heaviness}; as, buoyancy of spirits.
[1913 Webster]