sixth column

plural sixth columns

1. An additional group, beyond an identified fifth column, of people which clandestinely undermines a larger group, such as a nation, to which it is expected to be loyal.

   If the Government is talking about suppressing a Fifth Column, why raise a Sixth Column?

   1940 June 3, The Sun News-Pictorial, Melbourne, page 3, column 3

   1 more example

   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.

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

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