fron·tier /ˌfrʌnˈtɪr, ˈfrʌnˌ, frɑnˈ, ˈfrɑnˌ/
 國境,邊境;尚待開發的領域
 frontier
 邊緣
 frontier
 末梢
 frontier
 邊界
 Fron·tier 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. Fort. An outwork. [Obs.]
    Palisadoes, frontiers, parapets.   --Shak.
 Fron·tier, a.
 1. Lying on the exterior part; bordering; conterminous; as, a frontier town.
 2. Of or relating to a frontier. “Frontier experience.”
 Fron·tier, v. i. To constitute or form a frontier; to have a frontier; -- with on. [Obs.]
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 frontier
      n 1: a wilderness at the edge of a settled area of a country;
           "the individualism of the frontier in Andrew Jackson's
           day"
      2: an international boundary or the area (often fortified)
         immediately inside the boundary
      3: an undeveloped field of study; a topic inviting research and
         development; "he worked at the frontier of brain science"