(n.) That part of a country which fronts or faces another country or an unsettled region; the marches; the border, confine, or extreme part of a country, bordering on another country; the border of the settled and cultivated part of a country; as, the frontier of civilization.
(n.) An outwork.
(a.) Lying on the exterior part; bordering; conterminous; as, a frontier town.
(a.) Of or relating to a frontier.
(v. i.) To constitute or form a frontier; to have a frontier; -- with on.