By a person being childless (3)

I believe the answer is:

per

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'by' is the definition.
(I've seen this in another clue)

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

(Other definitions for per that I've seen before include "For each or every" , "Preposition meaning for each" , "According to" , "Preposition indicating by means of" .)

I've seen this clue in the Evening Standard.

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