Frontier

Part of speech: noun (n.)

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. An outwork. [Obs.] Palisadoes, frontiers, parapets. Shak.

Part of speech: verb (v.)

To constitute or form a frontier; to have a frontier; -- with on. [Obs.] Sir W. Temple.

Part of speech: adjective (a.)

1. Lying on the exterior part; bordering; conterminous; as, a frontier town.

2. Of or relating to a frontier. "Frontier experience." W. Irving.