fifth column
noun [ C ] uk/ˌfɪfθ ˈkɒl.əm/ us/ˌfɪfθ ˈkɑː.ləm/
第五纵队（支持并秘密帮助所在国家的敌人的一群人）
a group of people who support the enemies of the country they live in and secretly help them
fifth-columnist
noun [ C ] ukus
第五纵队队员
a member of such a group