early 15c., "land under the jurisdiction of a town, state, etc.," probably from Latin territorium "land around a town, domain, district," from terra "earth, land" (see terrain) + -orium, suffix denoting place (see -ory).
An alternative theory, somewhat supported by the vowels of the original Latin word, suggests derivation from terrere "to frighten" (see terrible); thus territorium would mean "a place from which people are warned off." Sense of "any tract of land, district, region" is first attested c.1600. Specific U.S. sense of "organized self-governing region not yet a state" is from 1799.