Stars, say, returning car (6)
I believe the answer is:
gemini
'stars' is the definition.
(constellation)
'say returning car' is the wordplay.
'say' becomes 'eg' (both can mean for example).
'returning' says the letters should be written in reverse.
'car' becomes 'mini' (Mini Cooper).
'eg' reversed gives 'ge'.
'ge'+'mini'='GEMINI'
(Other definitions for gemini that I've seen before include "Twins star sign" , "star group" , "Third zodiacal sign" , "Twins star-sign" , "lot of stars" .)