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"