Decline plate contaminated by something that's small (8)
I believe the answer is:
diminish
'decline' is the definition.
(I know that decline is a more specific form of diminish)
'plate contaminated by something that's small' is the wordplay.
I cannot really understand how this works, but
'small' could be 'mini' (short for miniature) and 'mini' is located in the answer.
'plate' could be 'dish' (type of plate) and 'dish' is located in the leftover letters.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for diminish that I've seen before include "cut down" , "Drop" , "make shorter" , "Make less with mini dish" , "sink" .)