Belittle; shrink (6)
I believe the answer is:
lessen
I believe this is a double definition.
'belittle' is the first definition.
(I've seen this in another clue)
'shrink' is the second definition.
(I've seen this before)
(Other definitions for lessen that I've seen before include "Cut back or diminish" , "Make smaller for lenses" , "Make smaller or fewer" , "Become smaller or fewer" , "Abate" .)