fifth column

Meaning

Noun

• A group of people which clandestinely undermines a larger group, such as a nation, to which it is expected to be loyal.

Origin

• 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 quinta columna consisting of his militant supporters within the capital, intent on undermining the Republican government from within.