Start angrily, perhaps, to harangue (3)

I believe the answer is:

nag

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'harangue' is the definition.
(I've seen this in another clue)

I don't understand how the remainder of the clue works.

(Other definitions for nag that I've seen before include "Old or over-worked horse" , "Horse; keep scolding" , "Henpeck, scold non-stop" , "Constant worrier" , "Keep worrying" .)

I've seen this clue in the Evening Standard.

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