A fashion editor's heavenly body (8)
I believe the answer is:
asteroid
'heavenly body' is the definition.
(asteroid is a kind of heavenly body)
'a fashion editor's' is the wordplay.
'fashion' indicates an anagram.
'editors' anagrammed gives 'steroid'.
'a'+'steroid'='ASTEROID'
(Other definitions for asteroid that I've seen before include "Small planet orbiting the Sun" , "Piece of rock that moves around the heavens" , "looking like a star?" , "could be dangerous for astronauts" , "Ceres, say" .)