1. a device designed to fit in each cylinder of a gasoline-powered internal-combustion engine and to produce the electric spark for igniting the mixture of gasoline and air.
2. Informal.a person who leads, inspires, or animates a group.
Pronunciation: (spärk'plug"), [key]
—v.t., -plugged, -plug•ging. Informal.
to lead, inspire, or animate something or someone.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.