NOUN (3)

1. a wilderness at the edge of a settled area of a country;
- Example: "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;
- Example: "he worked at the frontier of brain science"

The Collaborative International Dictionary of English v.0.48:

Frontier \Fron"tier\, n. [F. fronti[`e]re, 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.
      [1913 Webster]

   2. (Fort.) An outwork. [Obs.]
      [1913 Webster]

            Palisadoes, frontiers, parapets.      --Shak.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Frontier \Fron"tier\, a.
   1. Lying on the exterior part; bordering; conterminous; as, a
      frontier town.
      [1913 Webster]

   2. Of or relating to a frontier. "Frontier experience." --W.
      Irving.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Frontier \Fron"tier\, v. i.
   To constitute or form a frontier; to have a frontier; -- with
   on. [Obs.] --Sir W. Temple.
   [1913 Webster]

WordNet (r) 3.0 (2006):

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"

Moby Thesaurus II by Grady Ward, 1.0:

194 Moby Thesaurus words for "frontier":
   Berlin wall, China, Darkest Africa, God knows where, Greenland,
   North Pole, Outer Mongolia, Pago Pago, Pillars of Hercules,
   Siberia, South Pole, Thule, Tierra del Fuego, Timbuktu,
   Ultima Thule, Yukon, anteriority, antipodes, back country,
   backcountry, backwash, backwater, backwoods, bamboo curtain,
   bold front, boondock, boondocks, border, border ground,
   border line, bordering, borderland, borderline, bound, boundary,
   boundary condition, boundary line, bounding, bounds, bourn,
   brave face, brave front, break boundary, breakoff point, brush,
   bush, bush country, bushveld, ceiling, circumscription, coastal,
   compass, confine, cutoff, cutoff point, dark horse, deadline,
   delimitation, determinant, determinative, determining, display,
   division line, end, enigma, extreme, extremes, extremity, facade,
   face, facet, facia, finish, floor, fore, forefront, foreground,
   forehand, foreland, forepart, forequarter, foreside, forests,
   foreword, fringing, front, front elevation, front line, front man,
   front matter, front page, front view, frontage, frontal,
   frontier post, frontiers of knowledge, frontispiece,
   godforsaken place, hack, head, heading, hedge, high-water mark,
   hinterland, interface, iron curtain, jumping-off place, lap,
   limbic, limen, liminal, limit, limitation, limiting,
   limiting factor, limits, line, line of demarcation, littoral,
   low-water mark, lower limit, march, marches, marchland, marginal,
   mark, matter of ignorance, mete, mystery, n, nowhere, obverse,
   outback, outer space, outlandish, outpost, outskirts, pale, pole,
   preface, prefix, priority, proscenium, puzzle, remote, riddle,
   rimming, sealed book, skirting, start, starting line,
   starting point, sticks, target date, term, terminal, terminal date,
   terminus, terra incognita, the Great Divide, the South Seas,
   the boondocks, the bush, the incalculable, the moon, the sticks,
   the strange, the tullies, the unfamiliar, the unknowable,
   the unknown, three-mile limit, threshold, timbers, time allotment,
   twelve-mile limit, unexplored ground, unexplored territory,
   uninhabited region, unknown quantity, unsettled, up-country,
   upper limit, virgin land, virgin territory, wasteland, wild West,
   wilderness, wilds, window dressing, woodlands, woods, x, z



U.S. Gazetteer Counties (2000):

Frontier -- U.S. County in Nebraska
   Population (2000):    3099
   Housing Units (2000): 1543
   Land area (2000):     974.549525 sq. miles (2524.071575 sq. km)
   Water area (2000):    5.511605 sq. miles (14.274992 sq. km)
   Total area (2000):    980.061130 sq. miles (2538.346567 sq. km)
   Located within:       Nebraska (NE), FIPS 31
   Location:             40.549039 N, 100.401627 W
   Headwords:
    Frontier
    Frontier, NE
    Frontier County
    Frontier County, NE


U.S. Gazetteer Places (2000):

Frontier, ND -- U.S. city in North Dakota
   Population (2000):    273
   Housing Units (2000): 78
   Land area (2000):     0.179313 sq. miles (0.464419 sq. km)
   Water area (2000):    0.000000 sq. miles (0.000000 sq. km)
   Total area (2000):    0.179313 sq. miles (0.464419 sq. km)
   FIPS code:            28720
   Located within:       North Dakota (ND), FIPS 38
   Location:             46.800343 N, 96.833370 W
   ZIP Codes (1990):
   Note: some ZIP codes may be omitted esp. for suburbs.
   Headwords:
    Frontier, ND
    Frontier