The Collaborative International Dictionary of English v.0.48:

Pioneer \Pi`o*neer"\, n. [F. pionier, orig., a foot soldier, OF.
   peonier, fr. OF. peon a foot soldier, F. pion. See Pawn in
   chess.]
   1. (Mil.) A soldier detailed or employed to form roads, dig
      trenches, and make bridges, as an army advances.
      [1913 Webster]

   2. One who goes before, as into the wilderness, preparing the
      way for others to follow; as, pioneers of civilization;
      pioneers of reform.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Pioneer \Pi`o*neer"\, v. t. & i. [imp. & p. p. Pioneered; p.
   pr. & vb. n. Pioneering.]
   1. To go before, and prepare or open a way for; to act as
      pioneer.
      [1913 Webster]

   2. to take part in the early development of; to break ground
      in; to invent or originate.
      [PJC]

WordNet (r) 3.0 (2006):

pioneer
    n 1: someone who helps to open up a new line of research or
         technology or art [syn: pioneer, innovator,
         trailblazer, groundbreaker]
    2: one the first colonists or settlers in a new territory; "they
       went west as pioneers with only the possessions they could
       carry with them"
    v 1: open up an area or prepare a way; "She pioneered a graduate
         program for women students" [syn: pioneer, open up]
    2: take the lead or initiative in; participate in the
       development of; "This South African surgeon pioneered heart
       transplants" [syn: initiate, pioneer]
    3: open up and explore a new area; "pioneer space"

Moby Thesaurus II by Grady Ward, 1.0:

169 Moby Thesaurus words for "pioneer":
   Seabee, actuate, advance guard, adventurer, airhead, alpinist,
   ancestor, announcer, antecedent, astronaut, avant-garde,
   battle line, be in front, be the front-runner, beachhead, begin,
   bellwether, blaze the trail, break ground, break the ice,
   break the trail, bridgehead, buccinator, bushwhacker, camper,
   climber, coin, colonial, colonist, colonizer, combat engineer,
   comers and goers, commuter, cosmopolite, create, cruiser, develop,
   discover, earliest, engineer, establish, excursionist, explorer,
   fare, farthest outpost, first line, forebear, forefront, foregoer,
   forerun, forerunner, forge ahead, found, front, front line,
   front rank, front runner, front-runner, frontiersman, fugleman,
   globe-girdler, globe-trotter, go before, goer, groundbreaker,
   guide, hajji, harbinger, head, head up, herald, homesteader,
   immigrant, inaugurate, initial, initiate, innovate, innovator,
   institute, introduce, introduce new blood, invent, jet set,
   jet-setter, journeyer, kick off, launch, lay the foundation,
   lay the groundwork, lead, lead off, lead runner, lead the way,
   leader, line, maiden, make innovations, mariner, messenger,
   mountaineer, neologize, nester, open up, original, originate,
   outguard, outpost, pacemaker, palmer, passenger, passerby,
   pathfinder, pilgrim, pilot, planter, point, precede, precedent,
   precursor, predecessor, primary, prime, put in motion, railhead,
   revolutionize, rubberneck, rubbernecker, sailor, sapper,
   sapper and miner, scout, set in motion, set off, set up, settler,
   show the way, sightseer, sooner, spearhead, squatter, stand first,
   stand in front, start, stormy petrel, straphanger,
   take the initiative, take the lead, take the plunge, tourer,
   tourist, trailblazer, trailbreaker, transient, traveler, trekker,
   trend-setter, trigger, tripper, usher in, van, vanguard,
   vaunt-courier, viator, visiting fireman, voortrekker, voyager,
   voyageur, wayfarer, world-traveler



U.S. Gazetteer Places (2000):

Pioneer, OH -- U.S. village in Ohio
   Population (2000):    1460
   Housing Units (2000): 636
   Land area (2000):     1.601162 sq. miles (4.146990 sq. km)
   Water area (2000):    0.063282 sq. miles (0.163899 sq. km)
   Total area (2000):    1.664444 sq. miles (4.310889 sq. km)
   FIPS code:            62834
   Located within:       Ohio (OH), FIPS 39
   Location:             41.680569 N, 84.552796 W
   ZIP Codes (1990):     43554
   Note: some ZIP codes may be omitted esp. for suburbs.
   Headwords:
    Pioneer, OH
    Pioneer


U.S. Gazetteer Places (2000):

Pioneer, IA -- U.S. city in Iowa
   Population (2000):    21
   Housing Units (2000): 11
   Land area (2000):     0.063046 sq. miles (0.163289 sq. km)
   Water area (2000):    0.000000 sq. miles (0.000000 sq. km)
   Total area (2000):    0.063046 sq. miles (0.163289 sq. km)
   FIPS code:            62985
   Located within:       Iowa (IA), FIPS 19
   Location:             42.654422 N, 94.390775 W
   ZIP Codes (1990):
   Note: some ZIP codes may be omitted esp. for suburbs.
   Headwords:
    Pioneer, IA
    Pioneer


U.S. Gazetteer Places (2000):

Pioneer, LA -- U.S. village in Louisiana
   Population (2000):    171
   Housing Units (2000): 70
   Land area (2000):     1.088096 sq. miles (2.818156 sq. km)
   Water area (2000):    0.000000 sq. miles (0.000000 sq. km)
   Total area (2000):    1.088096 sq. miles (2.818156 sq. km)
   FIPS code:            60565
   Located within:       Louisiana (LA), FIPS 22
   Location:             32.736730 N, 91.434523 W
   ZIP Codes (1990):     71266
   Note: some ZIP codes may be omitted esp. for suburbs.
   Headwords:
    Pioneer, LA
    Pioneer