The Collaborative International Dictionary of English v.0.48:

Spearhead \Spear"head`\, n.
   The pointed head, or end, of a spear.
   [1913 Webster]

WordNet (r) 3.0 (2006):

spearhead
    n 1: someone who leads or initiates an activity (attack or
         campaign etc.)
    2: the leading military unit in an attack
    3: the head and sharpened point of a spear [syn: spearhead,
       spearpoint, spear-point]
    v 1: be the leader of; "She spearheaded the effort to find a
         cure for the disease"

Moby Thesaurus II by Grady Ward, 1.0:

49 Moby Thesaurus words for "spearhead":
   advance guard, airhead, avant-garde, battle line,
   be the bellwether, beachhead, beacon, blaze the trail,
   break the ice, bridgehead, cutting edge, farthest outpost,
   first line, forefront, front, front line, front rank, front-runner,
   get ahead of, get before, go before, guide, have the start, head,
   head the line, initiate, lap, launch, lead, lead the dance,
   lead the way, light the way, line, outguard, outpost, outstrip,
   pace, pioneer, point, precede, precursor, railhead, scout,
   set the pace, stand first, take the initiative, take the lead, van,
   vanguard