Right to avoid first medicinal herb (3)

I believe the answer is:

rue

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'herb' is the definition.
(I know that rue is a type of herb)

I cannot understand how the rest of the clue works.

(Other definitions for rue that I've seen before include "Regret or repent" , "Feel regret for the herb" , "Lament; a herb" , "Repentant sort of shrub?" , "Regret; road (Fr.)" .)

I've seen this clue in The Times.

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