IPA: //ʌnˈtruːθfəli//
KK: /ʌnˈtruːθfəli/
In a way that is not honest or true; by telling lies.
He answered the questions untruthfully, trying to hide the truth.
Untruthfully → It is formed from "un-" (meaning not) and "truth" (from Old English "triewð", meaning fidelity or truth) and "-fully" (meaning in a manner full of). The word "untruthfully" means in a manner that is not truthful or lacking in truth.
Think of 'not' ('un-') combined with 'truth' — this helps you remember that 'untruthfully' means acting in a way that is not truthful.