Peer in a legal office? How singular! (3,4)

I believe the answer is:

law lord

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

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

(Other definitions for law lord that I've seen before include "noble bigwig" , "peer into cases" , "Pre-August 2009, a member of the Appellate Committee of the Upper House" .)

I've seen this clue in the Evening Standard.

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