IPA: /ˈlaɪfˌlɔːŋ/
KK: /ˈlaɪfˌlɔŋ/
Something that lasts for the entire life of a person.
She has a lifelong passion for music that started when she was a child.
Lifelong → It is formed from "life" (from Old English "līf", meaning existence or living) and "long" (from Old English "lang", meaning extended in time or distance). The word "lifelong" means lasting for the duration of a person's life.
Think of 'life' as the time we exist and 'long' as something that extends over time — that's why lifelong means something that lasts for your entire life.