Speech about citadel (7)
I believe the answer is:
dialect
'speech' is the definition.
(dialect is a kind of speech)
'about citadel' is the wordplay.
'about' indicates an anagram.
'citadel' is an anagram of 'DIALECT'.
(Other definitions for dialect that I've seen before include "Regional form of speech" , "Manner of speaking" , "Local lingo" , "Regional language form" , "talk from the regions" .)