a military force that is raised from the civil population to supplement a regular army in an emergency.

〖通例the ～; 集合的に; 単複両扱い〗 民兵隊〘正規軍には属さず非常時のみ兵役に就く人からなる軍隊〙; 市民軍; 義勇軍; ｟米｠ 国民軍〘18—45歳の男子市民からなる〙; ｟米｠ 極右武装集団.

a military force that engages in rebel or terrorist activities in opposition to a regular army.

all able-bodied civilians eligible by law for military service.

late 16th century: from Latin, literally ‘military service’, from miles, milit- ‘soldier’.