IPA: /ʌnˈbiː.lɪf/
KK: /ʌnˈbɪlif/
A state of not believing or having faith, particularly in religious contexts.
His unbelief in the teachings of the church led him to seek answers elsewhere.
Unbelief is formed from "un-" (meaning not) and "belief" (from Old English "geleafa", meaning faith or trust). The word refers to the state of not having faith or trust in something.
Think of 'not' ('un-') having 'faith' ('geleafa') — that's why unbelief means a lack of faith.