Legion meaning : The major unit or division of the Roman army, usually comprising 3000 to 6000 infantry soldiers and 100 to 200 cavalry troops. A combined arms major military unit featuring cavalry, infantry, and artillery A large military or semi-military unit trained for combat; any military force; an army, regiment; an armed, organized and assembled militia. (often Legion or the Legion) A national organization or association of former servicemen, such as the American Legion. A large number of people; a multitude. (often plural) A great number. A group of orders inferior to a class; in scientific classification, a term occasionally used to express an assemblage of objects intermediate between an order and a class. To form into legions. Numerous; vast; very great in number