I. spear ‧ head 1 /ˈspɪəhed $ ˈspɪr-/ BrE AmE verb [transitive]
to lead an attack or organized action:
the troops who spearheaded the rescue mission
II. spearhead 2 BrE AmE noun [countable usually singular]
a person or group of people who lead an attack or organized action
spearhead of
The group became the spearhead of the labor union movement.