fifth column

American  

noun

1. a group of people who act traitorously and subversively out of a secret sympathy with an enemy of their country.

2. (originally) Franco sympathizers in Madrid during the Spanish Civil War: so called in allusion to a statement in 1936 that the insurgents had four columns marching on Madrid and a fifth column of sympathizers in the city ready to rise and betray it.

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fifth column British  

noun

1. (originally) a group of Falangist sympathizers in Madrid during the Spanish Civil War who were prepared to join the four columns of insurgents marching on the city

2. any group of hostile or subversive infiltrators; an enemy in one's midst

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fifth column Cultural  

1. People willing to cooperate with an aggressor against their own country. The term originated in a remark by Francisco Franco, the Spanish dictator, that he was marching on Madrid with four columns of troops, and that there was a “fifth column” of sympathizers within the city ready to help.

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fifth column Idioms  

1. 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.

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Other Word Forms

• fifth columnist noun

Example Sentences

In fact, because many children didn’t show symptoms of the infection or had only mild, flu-like symptoms, they functioned almost like an undetected fifth column in spreading the virus to adults.

From Los Angeles Times • Jun. 5, 2025

“We’re framed in this idea that somehow we’re a fifth column trying to take the country down,” said James Jones, vice chair of the board of the Islamic Seminary of America.

From Seattle Times • Feb. 18, 2020

I’ve found myself scrolling through her work, pausing every fourth or fifth column to read or reread her guidance on how to navigate the world.

From Washington Post • Jun. 25, 2019

KM: You referred to a movement as a fifth column.

From Salon • Jul. 20, 2017

Henry Reid advised employees to stay on the lookout for spies disguised as Langley Field soldiers and warned of fifth column plants who might coax valuable research from unwitting laboratory employees.

From "Hidden Figures" by Margot Lee Shetterly