Set fire to one outhouse - polished it off (9)

I believe the answer is:

burnished

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'polished it off' is the definition.
I can't tell whether this defines the answer.

'set fire to one outhouse' is the wordplay.
'set fire to' becomes 'burn' (I've seen this in another clue).
'one' becomes 'i' (Roman numeral).
'outhouse' becomes 'shed' (I've seen this in other clues).
'burn'+'i'+'shed'='BURNISHED'

Can you help me to learn more?

(Other definitions for burnished that I've seen before include "shone" , "made lustrous" .)

I've seen this clue in The Globe and Mail.

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