New military discipline ousting grand religious centre (7)
I believe the answer is:
nunnery
'religious centre' is the definition.
'new military discipline ousting grand' is the wordplay.
'new' becomes 'n'.
'military discipline' becomes 'gunnery'.
'ousting' indicates named letters should be taken away.
'grand' becomes 'g' ('G' can be a synonym of 'grand').
'gunnery' with 'g' removed is 'unnery'.
'n'+'unnery'='NUNNERY'
(Other definitions for nunnery that I've seen before include "Religious establishment" , "sisters' place" , "Hamlet to Ophelia: 'Get thee to a . . . . . . .'" , "Religious house for females" , "Convent" .)