An occasion of exemplary significance (8)

I believe the answer is:

instance

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

I cannot understand how the remainder of the clue works.

(Other definitions for instance that I've seen before include "An insect (anag.)" , "A case or example of something" , "Occasion" , "Canniest (anag) - occurrence" , "Case - isn't acne (anag)" .)

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

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