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.