Heavenly body with a tail (5)
I believe the answer is:
comet
'heavenly body with a tail' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for comet that I've seen before include "Celestial body - early jet aircraft" , "Heavenly body with a fiery tail" , "Celestial object" , "Orbiting extraterrestrial body" , "Heavenly visitor" .)