Agreement about attached string (7)

I believe the answer is:

concord

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'agreement' is the definition.
(I know that agreement can be written as concord)

'attached string' is the wordplay.
'attached' becomes 'con' (I can't explain this - if you can you should believe this answer much more).
'string' becomes 'cord' (I've seen this before).
'con'+'cord'='CONCORD'

'about' acts as a link.

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(Other definitions for concord that I've seen before include "Harmony; treaty" , "Agreement, harmony" , "Amity" , "Harmonious state of things" .)

I've seen this clue in The Daily Express.

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