(1):
(a.) Pertaining to, or engaged in, warfare carried on irregularly and by independent bands; as, a guerrilla party; guerrilla warfare.
(2):
(n.) An irregular mode of carrying on war, by the constant attacks of independent bands, adopted in the north of Spain during the Peninsular war.
(3):
(n.) One who carries on, or assists in carrying on, irregular warfare; especially, a member of an independent band engaged in predatory excursions in war time.