frontiern.[F. frontire, LL. frontaria. See Front.]1. 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.()2. (Fort.) An outwork.()Palisadoes, frontiers, parapets. (Shak.)a.1. Lying on the exterior part; bordering; conterminous; as, a frontier town.()2. Of or relating to a frontier.(W. Irving.)v. i. To constitute or form a frontier; to have a frontier; -- with on.(Sir W. Temple.)