Boring possibly but shrewd (11)

I believe the answer is:

penetrating

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'shrewd' is the definition.
(thesaurus)

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

(Other definitions for penetrating that I've seen before include "Going through" , "Boring - keen" , "Incisive" , "Acute" .)

I've seen this clue in The Globe and Mail.

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