No dinkum nurses fret behind shed (7)

I believe the answer is:

refusal

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'no' is the definition.
(refusing is saying no)

I cannot understand how the rest of the clue works.

(Other definitions for refusal that I've seen before include "Non-acceptance" , "The act of saying no" , "First this is first choice before others" , "Rejection; turning-down" , "Rebuff" .)

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

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