I. noun
or gue·ril·la gə-ˈri-lə, ge-, g(y)i-
Etymology: Spanish guerrilla, from diminutive of guerra war, of Germanic origin; akin to Old High German werra strife — more at war
Date: 1809
: a person who engages in irregular warfare especially as a member of an independent unit carrying out harassment and sabotage
II. adjective
Date: 1811
: of, relating to, or suggestive of guerrillas especially in being aggressive, radical, or unconventional