Main Entry: fifth column

Function: noun

Etymology: name applied to rebel sympathizers in Madrid in 1936 when four rebel columns were advancing on the city

Date: 1936

: a group of secret sympathizers or supporters of an enemy that engage in espionage or sabotage within defense lines or national borders

— fifth col·um·nism \-ˈkä-ləm-ˌ(n)i-zəm\ noun

— fifth col·um·nist \-(n)ist\ noun