Rogue has three keys (3)

I believe the answer is:

cad

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'rogue' is the definition.
(I've seen this in another clue)

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

(Other definitions for cad that I've seen before include "A rotter, by Jove" , "One behaves dishonourably" , "An Englishman who behaves dishonourably, a rotter" , "That ain't no gentleman" , "he's no gent" .)

I've seen this clue in The Mirror.

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