Is not wrong about the Army post (7)
I believe the answer is:
station
'post' is the definition.
('station' can be a synonym of 'post')
'is not wrong about the army' is the wordplay.
'wrong' indicates an anagram.
'about' is an insertion indicator.
'the army' becomes 'ta' (abbreviation for Territorial Army).
'is'+'not'='isnot'
'isnot' is an anagram of 'stion'.
'stion' placed around 'ta' is 'STATION'.
(Other definitions for station that I've seen before include "Nine across stop" , "eg Paddington" , "Broadcaster" , "Headquarters" , "Depot" .)