Possibly dialect for 'Keep' (7)
I believe the answer is:
citadel
'for keep' is the definition.
(I've seen this before)
'possibly dialect' is the wordplay.
'possibly' is an anagram indicator.
'dialect' is an anagram of 'CITADEL'.
(Other definitions for citadel that I've seen before include "Urban fortress" , "place of refuge" , "Fortress -- dialect (anag)" , "Highly-secure building" , "Urban stronghold - dialect (anag)" .)