means the act of setting something on fire or starting an engine's combustion, or the system in a vehicle that does so when you turn the key or press the button

from From Latin 'ignire,' to set on fire, built on 'ignis,' fire — the same root that gives us 'igneous' rocks born from molten heat. It entered English in the 1600s, long before there were engines to start, when it simply meant the kindling of flame; the automotive sense is a much later borrowing of that ancient fire-word for a new kind of controlled burning.