A moment of informality (5)

I believe the answer is:

jiffy

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'a moment' is the definition.
(I know that jiffy is a type of moment)

I don't understand the rest of the clue.

(Other definitions for jiffy that I've seen before include "Two shakes of a lamb's tail?" , "An instant" , "Moment (slang)" , "Very short moment - type of bag" , "Split second" .)

I've seen this clue in The Globe and Mail.

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