Light music to finish the day (4)
I believe the answer is:
airy
'light' is the definition.
(synonyms)
'music to finish the day' is the wordplay.
'music' becomes 'air' (air is a kind of music).
'to finish' suggests the final letters.
The final letter of 'day' is 'y'.
'air'+'y'='AIRY'
(Other definitions for airy that I've seen before include "Breezy" , "open to the sky" , "Flippant" , "Sprightly" , "Well-ventilated; delicate" .)