spearhead

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. The sharpened head of a spear.
2. n. The leading forces in a military thrust.
3. n. The driving force in a given action, endeavor, or movement.
4. v. To be the leader of (a movement, for example): "spearheaded the effort to offer classes in settlement houses [and] provide lecturers to women's clubs” ( Catherine Clinton).

Century Dictionary and Cyclopedia

1. n. The head of a spear. It is always pointed. and of iron or steel among people who know the use of iron, but anciently of bronze, and among some savage peoples of stone, bone or the like. The form varies from that of a long double-edged blade which with its socket is two feet or more in length, as was common in throwing-spears of the Franks and Saxons, to the head of the fourteenth-century lance, which was a mere pointing of the wooden shaft with steel and only a few inches in length. The spear-head is often barbed, sometimes serrated or wavy, etc. Compare coronal, 2, also pilum, lance, javelin.

Wiktionary

1. n. The pointed head, or end, of a spear.
2. n. One who leads or initiates an activity (such as an attack or a campaign).
3. n. The leading military unit in an attack.
4. n. sports A player who initiates attacking moves
5. v. transitive To drive or campaign ardently for, as an effort, project, etc.

GNU Webster's 1913

1. n. The pointed head, or end, of a spear.

WordNet 3.0

1. n. someone who leads or initiates an activity (attack or campaign etc.)
2. n. the head and sharpened point of a spear
3. v. be the leader of
4. n. the leading military unit in an attack