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Polish rival his nan upset (11)

Ross

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11

4,7

nailvarnish

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'polish' is the definition.
Both the answer and definition are adjectives.
Perhaps they are linked in a way I don't understand?

'rival his nan upset' is the wordplay.
'upset' indicates anagramming the letters.
'rival'+'his'+'nan'='rivalhisnan'
'rivalhisnan' anagrammed gives 'NAILVARNISH'.

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I've seen this clue in The Times.
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