It plays a starring role, but doesn't shine (6)
I believe the answer is:
planet
'it plays a starring role but doesn't shine' is the definition.
The definition suggests a singular noun which matches the answer.
'it plays a' is the wordplay.
I cannot quite see how this works, but
'it' could be 't' (abbreviation. e.g. in 'tis) and 't' is found in the answer.
'a' could be 'an' and 'an' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for planet that I've seen before include "Venus, for example" , "Substantial heavenly body" , "Celestial body that revolves around the sun" , "One orbiting star" , "Mercury?" .)