Dialect used in fortress (7)

I believe the answer is:

citadel

'fortress' is the definition.
(citadel can mean a fortified city)

'dialect used' is the wordplay.
'used' indicates an anagram.
'dialect' anagrammed gives 'CITADEL'.

'in' is the link.

(Other definitions for citadel that I've seen before include "Stronghold usually within the walls" , "Keep - castle" , "place of refuge" , "Kremlin" , "Stronghold (of the Salvation Army?)" .)

I've seen this clue in The Daily Express.

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