Buoyancy

1. n. Cheerfulness; vivacity; liveliness; sprightliness; — the opposite of heaviness; as, buoyancy of spirits.
2. n. 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.
3. n. 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.

The word meanings were obtained from OPTED(The Online Plain Text English Dictionary), which is based on “The Project Gutenberg Etext of Webster’s Unabridged Dictionary” which is in turn based on the 1913 US Webster’s Unabridged Dictionary (See Project Gutenburg), as a text file.