Be boastful at cards (4)

I believe the answer is:

brag

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'be boastful at cards' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.

This is the entire clue.

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(Other definitions for brag that I've seen before include "Blow one's own trumpet" , "game of bluff" , "Idle talk" , "Boast, exaggerate" , "Show off, crow" .)

I've seen this clue in the Evening Standard.

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