Sing door-to-door in December (5)
I believe the answer is:
carol
'sing door-to-door in december' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for carol that I've seen before include "Religious song - girl's name" , "Joyful religious song" , "Joyful song - girl's name" , "sing happily" , "Song celebrating the birth of Jesus" .)