Herb is an idiot! (4)

I believe the answer is:

dill

I'm a little stuck... Click here to teach me more about this clue!

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

I don't understand the remainder of the clue.

(Other definitions for dill that I've seen before include "Aromatic herb used as seasoning" , "Herb with feathery leaves and spicy seeds" , "Herb commonly used with gravlax" , "Herb used in cooking" , "Culinary herb" .)

I've seen this clue in the Sydney Morning Herald.

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