Make smaller vessel to carry small car (8)
I believe the answer is:
diminish
'make smaller' is the definition.
(diminishing is a kind of making smaller)
'vessel to carry small car' is the wordplay.
'vessel' becomes 'dish'.
'to carry' means one lot of letters goes inside another.
'small car' becomes 'mini' (I've seen this before).
'dish' enclosing 'mini' is 'DIMINISH'.
(Other definitions for diminish that I've seen before include "Grow smaller, shrink" , "Get smaller" , "Make or become smaller" , "Drop" , "Decrease, lessen" .)