/boy"euhn see, booh"yeuhn see/ , n.
1. the power to float or rise in a fluid; relative lightness.
2. the power of supporting a body so that it floats; upward pressure exerted by the fluid in which a body is immersed.
3. lightness or resilience of spirit; cheerfulness.
Also, buoyance .
[ 1705-15; BUOY(ANT) + -ANCY ]