Regret a somewhat rude utterance (3)

I believe the answer is:

rue

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'regret' is the definition.
(to rue something is to regret it)

I cannot understand how the remainder of the clue works.

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(Other definitions for rue that I've seen before include "Plant producing oil" , "repentance" , "Feel sorry" , "Regret - wild shrub" , "Regret the bitter herb" .)

I've seen this clue in the Evening Standard.

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