ignition

noun

1. (countable, uncountable)The act of igniting.
2. (countable, uncountable)The initiation of combustion.
3. (countable, uncountable)A system for activating combustion in a combustion engine.
4. (countable, uncountable)Receptacle for a key used to start the engine in a vehicle.

   “Put the key in the ignition and turn in right.”

5. (countable, uncountable)The phenomenon of a thermonuclear fusion reaction becoming self-sustaining and no longer requiring external heating.