Crossword Genius

Could mostly act deviously, unable to keep a secret (6)

Ross

I believe the answer is:

occult

'a secret' is the definition.
(I've seen this before)

I cannot understand how the remainder of the clue works.

(Other definitions for occult that I've seen before include "Esoteric, magical" , "Involving magical powers" , "Secret - paranormal" , "Secret - supernatural" , "Mystical, involving the supernatural" .)

I've seen this clue in The Times.
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