(~s)
1.
In a car engine, the ~ is the part where the fuel is ignited.
The device automatically disconnects the ~.
N-VAR
2.
Inside a car, the ~ is the part where you turn the key so that the engine starts.
N-SING: the N
3.
Ignition is the process of something starting to burn.
The ~ of methane gas killed eight men.
N-UNCOUNT