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early 14c., "country, territory, region," from Old French province "province, part of a country; administrative region for friars" (13c.) and directly from Latin provincia "territory outside Italy under Roman domination," also "a public office; public duty," of uncertain origin, usually explained as pro- "before" + vincere "to conquer" (see victor); but this does not suit the earliest Latin usages. Meaning "one's particular business or expertise" is from 1620s.
in Roman antiquity, a territorial subdivision of the Roman Empire-specifically, the sphere of action and authority of a Roman magistrate who held the imperium, or executive power. The name was at first applied to territories both in Italy and wherever else a Roman official exercised authority in the name of the Roman state. Later the name implied Roman possessions outside Italy from which tribute was required