New weaponry initially dropped in sister's home (7)
I believe the answer is:
nunnery
'sister's home' is the definition.
(nuns are known as sisters)
'new weaponry initially dropped' is the wordplay.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'weaponry' becomes 'gunnery' (gunnery is a kind of weaponry).
'initially dropped' means to remove the first letter.
'gunnery' with its initial letter removed is 'unnery'.
'n'+'unnery'='NUNNERY'
'in' acts as a link.
(Other definitions for nunnery that I've seen before include "Convent" , "Religious house for females" , "Hamlet to Ophelia: 'Get thee to a . . . . . . .'" , "Female religious house" , "sisters' place" .)