Webster's Revised Unabridged Dictionary · 1913

Frontier

Frontier , noun

[French frontière, Late Latin 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.
(Fortification) An outwork. [Obsolete]
Palisadoes, frontiers, parapets. — Shakespeare

Frontier , adjective

1.
Lying on the exterior part; bordering; conterminous; as, a frontier town.
2.
Of or relating to a frontier.
Frontier experience. — W. Irving

Frontier , intransitive verb

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