The Collaborative International Dictionary of English v.0.48:

Forerunner \Fore*run"ner\, n.
   1. A messenger sent before to give notice of the approach of
      others; a harbinger; a sign foreshowing something; a
      prognostic; as, the forerunner of a fever.
      [1913 Webster]

            Whither the forerunner in for us entered, even
            Jesus.                                --Heb. vi. 20.
      [1913 Webster]

            My elder brothers, my forerunners, came. --Dryden.
      [1913 Webster]

   2. A predecessor; an ancestor. [Obs.] --Shak.
      [1913 Webster]

   3. (Naut.) A piece of rag terminating the log line.
      [1913 Webster]

WordNet (r) 3.0 (2006):

forerunner
    n 1: a person who goes before or announces the coming of another
         [syn: precursor, forerunner]
    2: something that precedes and indicates the approach of
       something or someone [syn: harbinger, forerunner,
       predecessor, herald, precursor]
    3: anything that precedes something similar in time; "phrenology
       was an antecedent of modern neuroscience" [syn: antecedent,
       forerunner]

Moby Thesaurus II by Grady Ward, 1.0:

101 Moby Thesaurus words for "forerunner":
   Gabriel, Mahdi, advertisement, advertiser, ancestor, announcement,
   announcer, antecedent, augury, author, avant-garde, bell cow,
   bell mare, bellwether, born leader, buccinator,
   buccinator novi temporis, bushwhacker, charismatic leader,
   choirmaster, choragus, coach, conductor, coryphaeus, duce, envoy,
   evangel, evangelist, example, exemplar, explorer, file leader,
   forebear, forefather, foregoer, foreshadow, foreshadower,
   foretoken, forewarning, front runner, frontiersman, fugleman,
   groundbreaker, guide, harbinger, herald, herald angel, initiator,
   innovator, inspired leader, instructor, lead runner, leader,
   leader of men, mark, mentor, messenger, messiah, model, omen,
   originator, outrider, pacemaker, pacesetter, pathfinder, pattern,
   pioneer, point, portent, precedent, precentor, precursor,
   predecessor, premise, premonition, premonitor, preparationist,
   preparator, preparer, presage, presager, progenitor, prognostic,
   prototype, ringleader, scout, sign, standard-bearer, stormy petrel,
   symphonic conductor, symptom, teacher, token, torchbearer,
   trailblazer, trailbreaker, trainer, vanguard, vaunt-courier,
   voortrekker, warning



Easton's 1897 Bible Dictionary:

Forerunner
   John the Baptist went before our Lord in this character (Mark
   1:2, 3). Christ so called (Heb. 6:20) as entering before his
   people into the holy place as their head and guide.