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Related to fifth column: fifth estate
A clandestine group of people who work subversively within a group, organization, or country in order to betray it to an allied outside force. In the US during the Cold War, there was constant fear and suspicion of people supposedly working in a fifth column to spread the influence of communism from within.
A secret subversive group that works against a country or organization from the inside, as in The government feared that there was a fifth column working to oppose its policies during the crisis . This term was invented by General Emilio Mola during the Spanish Civil War in a radio broadcast on October 16, 1936, in which he said that he had una quinta columna ("a fifth column") of sympathizers for General Franco among the Republicans holding the city of Madrid, and it would join his four columns of troops when they attacked. The term was popularized by Ernest Hemingway and later extended to any traitorous insiders.
fifth columnan organized group of people sympathizing with and working for the enemy within a country at war or otherwise under attack.
Fifth column is a translation of the Spanish phrase quinta columna : during the Spanish Civil War, an extra body of supporters was claimed by General Mola as being within Madrid when he besieged the city with four columns of Nationalist forces in 1936 .