Fresh start for dimwit in Oz (5)

I believe the answer is:

ounce

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'oz' is the definition.
(I've seen this before)

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

(Other definitions for ounce that I've seen before include "Weight; big cat" , "Wild cat or light weight" , "Twelfth of a pound" , "On cue (anag.)" , "A light weight - feline" .)

I've seen this clue in The Times.

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