Collins Russian Dictionary 2nd Edition © HarperCollins Publishers 2000, 1997:
buoyant [ˈbɔɪənt] adj (ship) плаву́чий#; (economy, market) оживлённый*оживлён (prices, currency) твёрдый; (fig, person) жизнера́достный*жизнера́достен
* is used to mark translations which have irregular inflections. The Russian-English side of the dictionary gives inflectional information.