The Collaborative International Dictionary of English v.0.48:

Buoyant \Buoy"ant\, a. [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.
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   2. Bearing up, as a fluid; sustaining another body by being
      specifically heavier.
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            The water under me was buoyant.       --Dryden.
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   3. Light-hearted; vivacious; cheerful; as, a buoyant
      disposition; buoyant spirits. -- Buoy"ant*ly, adv.
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WordNet (r) 3.0 (2006):

buoyantly
    adv 1: in a cheerfully buoyant manner; "we accepted the
           opportunity buoyantly" [syn: buoyantly, chirpily]