Fortune I derive from pluckiest brat (4)

I believe the answer is:

pest

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

I don't understand the rest of the clue.

(Other definitions for pest that I've seen before include "Annoying creature" , "Troublesome person" , "Aphis" , "A nuisance - step on it" , "Destructive insect or nuisance" .)

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

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