Car limited by course that's lower (8)
I believe the answer is:
diminish
'that's lower' is the definition.
(thesaurus)
'car limited by course' is the wordplay.
'car' becomes 'mini' (Mini Cooper).
'limited by' means one lot of letters goes inside another (limit can mean to contain or border off).
'course' becomes 'dish' (I've seen this in another clue).
'mini' inserted into 'dish' is 'DIMINISH'.
(Other definitions for diminish that I've seen before include "Become smaller or less" , "Contract" , "Make or become smaller" , "Make smaller or less" , "Grow smaller, shrink" .)