IPA: /ɪɡˈnaɪtə/
KK: /ɪgˈnaɪtər/
A device or person that starts a fire or ignites something.
The ignitor sparked the flame in the furnace.
Ignitor is formed from "ignis" (meaning fire) and the suffix "-tor" (meaning one who). The word refers to one who ignites or sets something on fire.
Think of someone who brings 'fire' ('ignis') — that's why an ignitor is someone who ignites.