What is the meaning of Legion?

Numerous; vast; very great in number

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, including historical units such as the British Legion, and present-day units such as the Spanish Legion and the French Foreign Legion.

A large military or semi-military unit trained for combat; any military force; an army, regiment; an armed, organized and assembled militia.

A national organization or association of former servicemen, such as the American Legion.

A large number of people; a multitude.

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.

legion

accusative singular of legio

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Source: wiktionary.org