buoyant adj.

"float fixed in a place to indicate the position of objects underwater or to mark a channel," late 13c., boie, probably from Old French buie or Middle Dutch boeye, both of which likely are from Proto-Germanic *baukna- "beacon, signal" (see beacon). OED and Century Dictionary, however, suggest it is from Middle Dutch boeie or Old French boie "fetter, chain" (see boy), "because of its being fettered to a spot."

"buoyancy," 1806, from buoyant + -ance. The more usual word is buoyancy.

1713, "relative lightness, quality of floating on water or other liquid," from buoyant + -cy. The figurative sense "cheerfulness, hopefulness" (of spirits, etc.) is from 1819. The meaning "power of supporting a body so that it floats" is from 1831.