Dialect used in stronghold (7)
I believe the answer is:
citadel
'stronghold' is the definition.
(citadel is a kind of stronghold)
'dialect used' is the wordplay.
'used' indicates anagramming the letters.
'dialect' anagrammed gives 'CITADEL'.
'in' is the link.
(Other definitions for citadel that I've seen before include "where Salvationists meet" , "place of refuge" , "Highly-secure building" , "Fortress -- dialect (anag)" , "Bastion" .)