Crossword Genius

Lung? Unsure — rib possibly (3,2,4)

Ross

I believe the answer is:

rus in urbe

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'lung?' is the definition.
I know nothing about this answer so I can't judge whether this works.

'unsure rib possibly' is the wordplay.
'possibly' indicates anagramming the letters.
'unsure'+'rib'='unsurerib'
'unsurerib' is an anagram of 'RUS IN URBE'.

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I've seen this clue in The Times and The Sunday Times.
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