Fighter, perhaps with bit of tan and heavenly body (6)
I believe the answer is:
planet
'heavenly body' is the definition.
(planet is a kind of heavenly body)
'fighter perhaps with bit of tan' is the wordplay.
'fighter perhaps' becomes 'plane' (fighter is a kind of plane).
'with' says to put letters next to each other.
'bit of' indicates taking the first letters.
The first letter of 'tan' is 't'.
'plane'+'t'='PLANET'
'and' acts as a link.
(Other definitions for planet that I've seen before include "Celestial body orbiting round a star" , "World" , "Mars or Uranus" , "Heavenly (or earthly!) body" , "Large body orbiting sun" .)