Unusual way to serve meat (4)

I believe the answer is:

rare

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

I cannot understand how the rest of the clue works.

(Other definitions for rare that I've seen before include "(Of meat) red" , "Might steak be" , "Rear up, being scarce" , "Scarce as hen's teeth!" , "Very infrequent, lightly cooked" .)

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

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