IPA: /ˈvɛn.dʒfəl.i/
KK: /ˈvɛnʤfəli/
In a way that shows a desire for revenge or to harm someone because of a wrong done to oneself.
She acted vengefully after being betrayed by her friend.
Vengefully → It is formed from "venge" (from Old French *venger*, meaning to take revenge) and "-fully" (meaning in a manner full of). The word "vengefully" means in a manner full of revenge or with the intent to take revenge.
Think of acting 'in a manner full of' revenge — 'venge' relates to taking revenge, and '-fully' indicates the way of doing it.