IPA: /ɪnˈkrɛdʒ.ʊl.ɪ.ti/
KK: /ɪnˈkrɛdʒʊlɪti/
The feeling of not being able to believe something; doubt about the truth of something.
She looked at him in incredulity when he told her the news.
Incredulity → It is formed from "in-" (meaning not) and "credulus" (from Latin, meaning believing). The word describes a state of not believing or being unwilling to believe something.
Think of 'not' ('in-') being able to 'believe' ('credulus') — that's why incredulity means a lack of belief.