Light-hearted (7)
'light-hearted' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for playful that I've seen before include "Frolicsome" , "Teasing, unserious" , "Frisky" , "Full of fun" , "Fun-loving" .)
(Other definitions for thaw that I've seen before include "spring weather?" , "Melt in heat" , "John, once regularly on TV" , "the end of a white Christmas?" , "(Of ice/snow) melt" .)