Member of an irregular armed force (8)
I believe the answer is:
guerilla
'member of an irregular armed force' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for guerilla that I've seen before include "Insurgent who works through sabotage and harassment" , "Freedom fighter" , "One of small independent group of fighters" , "He fights as part of small independent group" , "Member of irregular armed force" .)