Character inside citadel talking (5)
I believe the answer is:
delta
'character' is the definition.
(delta is a kind of character)
'inside citadel talking' is the wordplay.
'inside' indicates a hidden word.
'DELTA' is hidden in the letters of 'citadel talking'.
(Other definitions for delta that I've seen before include "Wing shape; Greek D" , "Comms code for 'd'" , "Alluvial area - Greek letter" , "Alluvial river mouth" , "Fragmented estuary" .)