From WordNet (r) 2.0 (August 2003) [wn]:
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: spearpoint,
spear-point]
v : be the leader of; "She spearheded the effort to find a cure
for the disease"
From The Collaborative International Dictionary of English v.0.48 [gcide]:
Spearhead \Spear"head`\, n.
The pointed head, or end, of a spear.
[1913 Webster]