1. In ancient Rome, a Roman army division of 3 000 to 6 000 soldiers, including cavalry.
2. A large number of people or things.
3. An association of ex-servicemen and ex-service women.
4. Etymology: from Old French legion, "Roman legion" (3,000 to 6,000 men, under Marius usually with attached cavalry); from Latin legionem, legio, "body of soldiers"; from legere, "to choose, to gather"; also "to read".