Alarmist in Greece mostly involved with Romans (11)
I believe the answer is:
scaremonger
'alarmist' is the definition.
(scaremonger is a kind of alarmist)
'greece mostly involved with romans' is the wordplay.
'mostly' means to remove the last letter (most but not all of the word).
'involved with' indicates an anagram (involved can mean confusing or complex).
'greece' with its final letter taken off is 'greec'.
'greec' anagrammed with 'romans' can make 'SCAREMONGER'.
'in' acts as a link.
(Other definitions for scaremonger that I've seen before include "Spreader of frightening rumours" , "Spreader of panic" , "One spreading worrying rumours" , "agitator" , "Alarmist" .)