IPA: /ˈɪn.fə.məs/
KK: /ˈɪn.fə.məs/
Having a very bad reputation, often because of a crime or wrongdoing.
The infamous criminal was finally caught after years of evading the police.
Infamous is formed from "in-" (meaning not) and "fama" (meaning fame or reputation). The word describes someone who is not famous for good reasons, but rather has a bad reputation.
Think of someone who is 'not' ('in-') known for good things ('fama') — that's why infamous means having a bad reputation.