So to speak, one's best, best friend (4)

I believe the answer is:

peke

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'so' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for peke that I've seen before include "Small breed of dog" , "Breed of dog (shortened)" , "Sort of lapdog" , "Small canine" , "Little dog" .)

I've seen this clue in the Evening Standard.

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