(also guer·illa ) / gəˈrɪlə; NAmE / noun
a member of a small group of soldiers who are not part of an official army and who fight against official soldiers, usually to try to change the government :
urban guerrillas (= those who fight in towns)
guerrilla war / warfare (= fought by guerrillas on one or both sides)
a guerrilla movement
—compare freedom fighter
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WORD ORIGIN
early 19th cent. (introduced during the Peninsular War): from Spanish , diminutive of guerra war.