Crossword Genius

Sylvester is briefly crafty (3)

Ross

I believe the answer is:

sly

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'crafty' is the definition.
(synonyms)

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

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(Other definitions for sly that I've seen before include "Unpleasantly cunning and secretive" , "'Cunning, wily (3)'" , "Cunning; surreptitious" , "Crafty, devious" , "'Crafty, cunning (3)'" .)

I've seen this clue in The Mirror.
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