A banned body builder with a heavenly body (8)
I believe the answer is:
asteroid
'a heavenly body' is the definition.
(asteroid is a kind of heavenly body)
'a banned body builder' is the wordplay.
I cannot quite see how this works, but
'a' is present in the answer.
The remaining letters 'steroid' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
'with' is the link.
Can you help me to learn more?
(Other definitions for asteroid that I've seen before include "space traveller" , "Lump of rock orbiting the sun" , "Small rocky object orbiting the sun - store aid (anag)" , "way-out rock" , "could be dangerous for astronauts" .)