Conclude it's a coating of some kind (6)

I believe the answer is:

finish

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'conclude' is the definition.
(I've seen this before)

I cannot understand how the remainder of the clue works.

(Other definitions for finish that I've seen before include "End, conclusion" , "Polish, perhaps" , "Treatment of surface" , "End, complete" , "curtains" .)

I've seen this clue in the Evening Standard.

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