fifth column

• 5th column

From a 1936 radio address by Spanish Nationalist general Emilio Mola, in which he spoke of four of his army columns moving on Madrid and a fifth column (quinta columna) consisting of his militant supporters within the capital, intent on undermining the Republican government from within.

fifth column (plural fifth columns)

1. A group of people which clandestinely undermines a larger group, such as a nation, to which it is expected to be loyal.
   • 1939 March 29, “Madrid gives itself up to Franco”, in The Guardian‎^[1], →ISSN:

     The rebels, who in November 1936 had fought to enter and failed, walked in yesterday as troops of the generally recognised Spanish Government, and not a shot was fired at them. The supporters of Franco in the city, the “fifth column” he once spoke of, had been waiting for this moment for more than two years.

   • 1940 September 20, The Advertiser, Adelaide, page 24, column 4:

     True, we have people of the fifth column, and, unfortunately, the sixth column, with us; they have them in every country; but so far in this war the British diplomatic and secret service has not been so successful as that clever, astute brute-man Hitler and his agents.

   • 2020 January 2, Conrad Landin, “Strife and strikes in post-war Britain”, in Rail, page 52:

     Lloyd George's belief in a revolutionary fifth column [the term hadn't been coined then] driving the strike was replicated on Fleet Street. On October 1 [1919] The Times thundered: "The attempt of the strike leaders to subvert Constitutional government in this country and to starve the nation into acquiescence in their revolutionary designs will be defeated, as other onslaughts have been defeated, by the firmness of the people in defence of its liberties."

2. Used other than figuratively or idiomatically: see fifth,‎ column.

• fifth columnism
• fifth columnist

• agent provocateur
• Trojan horse