Turn over secure weapons (4)
I believe the answer is:
guns
'weapons' is the definition.
(gun is a kind of weapon)
'turn over secure' is the wordplay.
'turn over' says the letters should be written in reverse.
'secure' becomes 'snug' ('snug' can be similar in meaning to 'secure').
'snug' backwards is 'GUNS'.
(Other definitions for guns that I've seen before include "Transportable armaments" , "Snug weapons?" , "Bangers" , "Firearms" .)