IPA: /ɪnˈkrɛdʒ.ə.ləs.li/
KK: /ɪnˈkrɛdʒələsli/
In a way that shows you do not believe something is true or real.
She looked at him incredulously when he told her the news.
Incredulously → It is formed from "in-" (meaning not) and "credulus" (from Latin, meaning believing) and the suffix "-ly" (meaning in a manner). The word describes a manner of not believing or being skeptical about something.
Think of 'not believing' ('in-') and 'believing' ('credulus') to remember that 'incredulously' means to do something in a way that shows disbelief.