Tip of a comet (4)
I believe the answer is:
tail
'tip of a comet' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for tail that I've seen before include "Rear appendage of animal" , "Follow - dog" , "Elongated appendage of an animal" , "Trail (behind comet)" , "Caudal fin" .)