Fears nearly all weapons (6)
I believe the answer is:
alarms
'fears' is the definition.
(alarm is a kind of fear)
'nearly all weapons' is the wordplay.
'nearly all' becomes 'al'.
'weapons' becomes 'arms' ('arm' can be a synonym of 'weapon').
'al'+'arms'='ALARMS'
(Other definitions for alarms that I've seen before include "Warning clocks that wake us up" , "Frightens, scares" , "Alerting devices - burglars?" , "Disturbs" , "Scares or startles" .)