ignition

Short definition from Wiktionary

Noun

1. 1
   The act of igniting.
2. 2
   The initiation of combustion.
3. 3
   A system for activating combustion in a combustion engine.
4. 4
   Receptacle for a key used to start the engine in a vehicle.
5. 5
   The phenomenon of a thermonuclear fusion reaction becoming self-sustaining and no longer requiring external heating.