It's sound in diplomacy (6)

I believe the answer is:

intact

'it's sound' is the definition.
(I've seen this in another clue)

'in diplomacy' is the wordplay.
'diplomacy' becomes 'tact' (tact can mean diplomacy or sensitivity).
'in'+'tact'='INTACT'

(Other definitions for intact that I've seen before include "Flawless" , "Whole and complete" , "Entire, untouched" , "Unscathed" , "Complete - unbroken" .)

I've seen this clue in The Globe and Mail.

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