frontier

Etymology

From Middle English frounter, from Old French fronter (whence Modern French frontière), from front.

noun

1. The part of a country which borders or faces another country or unsettled region.
   From time to time the coaches of the Lötschberg Railway itself, which in comfort and décor can rank with the finest in Europe today, travel far from the frontiers of Switzerland on through workings such as these. 1960 December, Cecil J. Allen, “Operating a mountain main line: the Bern-Lötschberg-Simplon: Part One”, in Trains Illustrated, page 743
   Unlike a boundary, which evokes the image of a line on a map and demarcates spheres of political control, the frontier is an area where colonisation is taking place....no authority is recognised as legitimate by all parties or is able to excersise undisputed control over the area. 1979, Richard Elphic, Hermann Guilomee (editors), The shaping of South African Society, 1652 - 1820, page 297
2. The most advanced or recent version of something; leading edge.
   the frontier of civilization
3. (obsolete) An outwork of a fortification.

verb

1. (intransitive) To live as pioneers on frontier territory.
2. (transitive, obsolete) To place on the frontier.