Lovely day to play with R.E.M. (6)
I believe the answer is:
dreamy
'lovely' is the definition.
(I've seen this before)
'day to play with r e m' is the wordplay.
'to play with' indicates an anagram.
'r'+'e'+'m'='rem'
'day' anagrammed with 'rem' makes 'DREAMY'.
(Other definitions for dreamy that I've seen before include "Descriptive of the music of a nocturne" , "delightful" , "Misty" , "My dear (anag.)" , "like a midsummer night?" .)