Couple in the back of huge car could be stars (6)
I believe the answer is:
gemini
'be stars' is the definition.
(constellation)
'couple in the back of huge car' is the wordplay.
'couple in' becomes 'g' (I can't explain this - if you can you should give a lot more credence to this answer).
'the back of' indicates one should take the final letters.
'car' becomes 'mini' (Mini Cooper).
The last letter of 'huge' is 'e'.
'g'+'e'+'mini'='GEMINI'
'could' is the link.
Can you help me to learn more?
(Other definitions for gemini that I've seen before include "star group" , "set of twinklers" , "Third zodiacal sign" , "lot of stars" , "Zodiac sign - the Twins" .)