Very happy or cheerful (6)
I believe the answer is:
blithe
I believe this clue is a double definition.
'very happy' is the first definition.
(I've seen this before)
'cheerful' is the second definition.
(similar in meaning)
(Other definitions for blithe that I've seen before include "Heedless" , "light" , "Light-hearted and good-humoured" , "Innocently happy" , "Merry" .)