(1):
(v. t. & i.) Light-hearted; vivacious; cheerful; as, a buoyant disposition; buoyant spirits.
(2):
(v. t. & i.) Bearing up, as a fluid; sustaining another body by being specifically heavier.
(3):
(v. t. & i.) Having the quality of rising or floating in a fluid; tending to rise or float; as, iron is buoyant in mercury.