IPA: /ˈʌn.lɪt/
KK: /ʌnˈlɪt/
Not illuminated or not having any light.
The room was unlit, making it difficult to see anything inside.
Unlit → It is formed from "un-" (meaning not) and "lit" (the past participle of "light", meaning to illuminate). The word "unlit" means not illuminated or without light.
Think of 'not' ('un-') having 'light' — that's why unlit means something that is not illuminated.