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Synonyms for Buoyant (same or very similar meaning)

WordNet sense 1 (tending to float on a liquid or rise in air or gas):

WordNet sense 2 (characterized by liveliness and lightheartedness):
perky, chirpy

WordNet sense 3 (being full of or promoting cheer; having or showing good spirits):

From the ODE community, based on WordNetadd/edit