IPA: //ʌnˈdjuːtɪfəl//
KK: /ʌnˈdjuːtɪfəl/
Not showing a sense of responsibility or duty; failing to fulfill obligations or expectations.
The undutiful son often ignored his parents' advice and responsibilities.
Undutiful → It is formed from "un-" (meaning not) and "dutiful" (from "duty" which comes from Old French *devoir*, meaning obligation or responsibility). The word "undutiful" means not fulfilling one's duty or obligation.
Think of 'not' ('un-') fulfilling an 'obligation' ('duty') — that's why undutiful means failing to meet one's responsibilities.