Scaremonger's weapon in atomic schedule (8)
I believe the answer is:
alarmist
'scaremonger's' is the definition.
(I've seen this before)
'weapon in atomic schedule' is the wordplay.
'weapon' becomes 'arm' (I've seen this before).
'in' indicates putting letters inside.
'atomic' becomes 'a' (eg in A-test, atomic test).
'schedule' becomes 'list' (I've seen this in other clues).
'a'+'list'='alist'
'arm' inserted within 'alist' is 'ALARMIST'.
(Other definitions for alarmist that I've seen before include "One who exaggerates a danger" , "unduly frightening" , "Person exaggerating danger" , "Spreader of panic" , "Person frightening others needlessly" .)