Item left in car with sloping roof (6)
I believe the answer is:
couple
'item' is the definition.
(I've seen this before)
'left in car with sloping roof' is the wordplay.
'left' becomes 'l' (common abbreviation).
'in' is an insertion indicator.
'car with sloping roof' becomes 'coupe' (a coupe is a car with a sloping roof).
'l' placed into 'coupe' is 'COUPLE'.
(Other definitions for couple that I've seen before include "Unite" , "item" , "Two of a kind" , "Link together - say two married people" , "Pair, duo" .)