Something you'll want to polish off, on your plate (7)
I believe the answer is:
tarnish
'plate' is the definition.
The answer and definition can be both to do with contact as well as being verbs in their base form.
Maybe there's a link between them I don't understand?
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for tarnish that I've seen before include "Discolouration of metal surface" , "Discolour - sully" , "Taint" , "Stain or blemish, silver or reputation" , "Mountain lake" .)