guer ‧ ril ‧ la /ɡəˈrɪlə/ BrE AmE noun [countable]
[ Date: 1800-1900 ; Language: Spanish ; Origin: guerra 'war' ]
a member of a small unofficial military group that fights in small groups
guerrilla war/warfare
American troops found themselves fighting a guerrilla war.
left-wing guerrillas