What does "department" mean?

Additional senses

1. 2.A distinct course of life, action, study, or the like; appointed sphere or walk; province. Superior to Pope in Pope's own peculiar department of literature. Macaulay.
2. 3.Subdivision of business or official duty; especially, one of the principal divisions of executive government; as, the treasury department; the war department; also, in a university, one of the divisions of instructions; as, the medical department; the department of physics.
3. 4.A territorial division; a district; esp., in France, one of the districts composed of several arrondissements into which the country is divided for governmental purposes; as, the Department of the Loire.
4. 5.A military subdivision of a country; as, the Department of the Potomac.