a subversive group that supports the enemy and engages in espionage or sabotage; an enemy in your midst
例句
用作名词 (n.)
Beware of the fifth column. They often infiltrate into key positions and seek to undermine the body politic from within. 要提防隐蔽的敌人，他们经常渗透到关键岗位企图从内部破坏国家政体。
美
