One picked for concert? (6)

I believe the answer is:

guitar

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

I don't understand the remainder of the clue.

Can you help me to learn more?

(Other definitions for guitar that I've seen before include "Talk under one's breath" , "Instrument played by Django Reinhardt" , "Stringed instrument often played by pop groups" , "13's lute" , "Popular stringed musical instrument" .)

I've seen this clue in The Sun.

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