Tending to keep one's activities dark (5)

I believe the answer is:

shady

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'dark' is the definition.
(similar in meaning)

I don't understand the remainder of the clue.

(Other definitions for shady that I've seen before include "Suspicious, fishy" , "Of questionable morality out of the sunlight" , "Disreputable - umbrageous" , "Of doubtful honesty" , "Of dubious legality" .)

I've seen this clue in the Evening Standard.

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