Saylor __________________ fifth column __________________ noun A clandestine subversive organization working within a country to further an invading enemy's military and political aims. A group of persons inside the battle lines of a territory engaged in a conflict, who secretly sympathize with the enemy, and who engage in espionage or sabotage; -- sometimes also referred to as a trojan horse. Hence, any faction of persons within a group who secretly sympathize with an enemy, especially those who engage in activities harmful to the group; an enemy in one's midst; a group of traitors. A group of people which clandestinely undermines a larger group, such as a nation, to which it is expected to be loyal. A subversive group that supports the enemy and engages in espionage or sabotage; an enemy in your midst.