Buoyant, a.
Etymology: [From Buoy, v. t. & i.]
1. Having the quality of rising or floating in a fluid; tending to rise or float; as, iron is buoyant in mercury. "Buoyant on the flood." Pope.
2. Bearing up, as a fluid; sustaining another body by being specifically heavier. The water under me was buoyant. Dryden.
3. Light-hearted; vivacious; cheerful; as, a buoyant disposition; buoyant spirits. -- Buoy"ant*ly, adv.