Gay (5)
'gay' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for blithe that I've seen before include "Innocently happy" , "'Hail to thee, ,,,,,, spirit'- Shelley (6)" , "Shelley: 'Hail to thee . . . . . . spirit! Bird thou never wert'" , "With neither worries nor cares" , "Happy, without worries or cares" .)
'gay' is the definition.
(synonyms)
This is all the clue.
(Other definitions for merry that I've seen before include "Joyous; tipsy (colloq.)" , "Jolly and gay" , "Lively -- slightly drunk" , "Full of fun and gaiety" , "Operetta by 11" .)