One choosing to be more generously proportioned? (7)

I believe the answer is:

plumper

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

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

I don't understand the remainder of the clue.

(Other definitions for plumper that I've seen before include "One choosing" , "Fuller and rounder" , "more stout" .)

I've seen this clue in The Everyman puzzle in The Observer.

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