IPA: /ˌdɛbəˈnɛrli/
KK: /ˈdɛbəˌnɛrli/
In a charming and confident way, often associated with elegance and sophistication.
He walked debonairly into the room, catching everyone's attention with his style.
Debonairly is formed from "debonair" (from Old French *debonnaire*, meaning courteous or gracious) and the adverbial suffix "-ly" (meaning in a manner of). The word describes a manner that is courteous, gracious, or charming.
Think of someone being 'courteous' and 'gracious' ('debonair') in their actions, and the '-ly' shows how they do it — that's why debonairly means doing something in a charming and gracious way.