IPA: /ˈhɛlˌfaɪər/
KK: /hɛlˌfaɪər/
A type of fire associated with hell, often thought of as a place of punishment for those who have sinned.
In many religious beliefs, hellfire is seen as a consequence for wrongdoing in life.
Hellfire → The word is formed from "hell" (from Old English *hel*, meaning the underworld or a place of torment) and "fire" (from Old English *fyr*, meaning flame or burning). Together, they describe the flames associated with the underworld or a place of eternal punishment.
Imagine the 'underworld' ('hell') filled with 'flames' ('fire') — that's why hellfire refers to the burning associated with hell.