Bright boy (3)

I believe the answer is:

ray

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'boy' is the definition.

I don't understand how the remainder of the clue works.

(Other definitions for ray that I've seen before include "Flatfish or sunbeam" , "Lindwall" , "Broad flat fish; beam" , "A little light" , "Flash < Movie Player" .)

I've seen this clue in the Evening Standard.

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