A black eye, it seems, shows brilliance! (6)

I believe the answer is:

shiner

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'a black eye' is the definition.
(I know that black eye can be written as shiner)

I cannot understand how the rest of the clue works.

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(Other definitions for shiner that I've seen before include "A black eye, colloquially" , "injury to face?" , "Black eye - small glittering fish" , "What one might get from boxer" , "Informally, a black eye" .)

I've seen this clue in the Evening Standard.

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