Department

noun

1. A part, portion, or subdivision.
2. A distinct course of life, action, study, or the like.

   "Technical things are not his department; he's a people person."

3. A subdivision of an organization.
4. A territorial division; a district; especially, in France, one of the districts into which the country is divided for governmental purposes, similar to a county in the UK and in the USA. France is composed of 101 départements organized in 18 régions, each department is divided into arrondissements, in turn divided into cantons.
5. A military subdivision of a country

   "the Department of the Potomac"