The Collaborative International Dictionary of English v.0.48:

Frontiersman \Fron"tiers*man\, n.; pl. Frontiersmen.
   A man living on the frontier. Frontignac

WordNet (r) 3.0 (2006):

frontiersman
    n 1: a man who lives on the frontier [syn: frontiersman,
         backwoodsman, mountain man]

Moby Thesaurus II by Grady Ward, 1.0:

52 Moby Thesaurus words for "frontiersman":
   ancestor, announcer, antecedent, avant-garde, backwoodsman,
   bellwether, briar-hopper, brush ape, buccinator, bushman,
   bushwhacker, clam digger, cracker, desert rat, explorer, forebear,
   foregoer, forerunner, forester, front runner, fugleman,
   groundbreaker, guide, harbinger, herald, hillbilly, hinterlander,
   innovator, lead runner, leader, messenger, mountain man,
   mountaineer, pathfinder, piny, pioneer, point, precedent,
   precursor, predecessor, redneck, ridge runner, scout,
   stormy petrel, trailblazer, trailbreaker, vanguard, vaunt-courier,
   voortrekker, woodlander, woodman, woodsman