Perfect advice for a peeping Tom? (8)

I believe the answer is:

peerless

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'perfect' is the definition.
(thesaurus)

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

(Other definitions for peerless that I've seen before include "Without equal, nonpareil" , "Beyond compare" , "Unrivalled" , "Unparalleled, incomparable" , "Without equal or lacking lords" .)

I've seen this clue in The Times.

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