Unfinished business in den, possibly? (5,3)

I believe the answer is:

loose end

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'unfinished business' is the definition.
(synonyms)

I can't explain the rest of the clue.

(Other definitions for loose end that I've seen before include "'A detail not settled or explained (5,3)'" , "The bored, idle at one" , "Detail not yet settled" , "should have been tied?" , "As yet unexplained detail" .)

I've seen this clue in The Telegraph.

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