Crossword Genius

Obtain by duplication? (3)

Ross

I believe the answer is:

buy

I'm a little stuck... Click here to teach me more about this clue!

This could be a double definition.

'obtain' is the first definition.
(thesaurus)

'duplication?' is the second definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.

'by' acts as a link.

Can you help me to learn more?

(Other definitions for buy that I've seen before include "Get" , "Procure" , "Purchase" , "Accept truth of (colloq.)" .)

I've seen this clue in the Evening Standard.
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