fifth column

Fifth column, a translation of the Spanish quinta columna, was inspired by a boast by rebel general Emilio Mola during the Spanish Civil War. Mola predicted Madrid would fall as four columns of rebel troops approaching the city were joined by another hidden column of sympathizers within it. In an October 1936 article in The New York Times, William Carney described those secret rebel supporters as the "fifth column," and English speakers seized upon the term. It gained widespread popularity after Ernest Hemingway used it in the title of a 1938 book, and it was often applied (along with derivative forms such as "fifth columnism" and "fifth columnist") to Nazi supporters within foreign nations during World War II.