Merit retained by nuclear nations (4)

I believe the answer is:

earn

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

'merit' is the definition.
(I've seen this in other clues)

'retained by nuclear nations' is the wordplay.
'EARN' is hidden in amongst the letters.
But, I'm uncertain how the hidden word is indicated.

Can you help me to learn more?

(Other definitions for earn that I've seen before include "Receive in return for" , "Attain" , "net" , "Take in bread" , "Acquire through merit" .)

I've seen this clue in The Times.

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