Heavenly bodies a hormone finally produces (9)
I believe the answer is:
asteroids
'heavenly bodies' is the definition.
(asteroid is a kind of heavenly body)
'a hormone finally produces' is the wordplay.
'hormone' becomes 'steroid' (steroid hormone is a kind of hormone).
'finally' says to take the final letters.
The last letter of 'produces' is 's'.
'a'+'steroid'+'s'='ASTEROIDS'
(Other definitions for asteroids that I've seen before include "Small celestial bodies that move around the sun" , "lumps of rock" , "Small planets orbiting the sun" , "Heavenly bodies" , "Do satires address small planets?" .)