IPA: /ˈlɔːfəli/
KK: /ˈlɔːfəli/
In a way that is allowed by the law; legally.
The company operates lawfully and follows all regulations.
Lawfully → It is formed from "law" (from Old English *lagu*, meaning a rule or regulation) and "-fully" (meaning in a manner full of or characterized by). The word "lawfully" means in a manner that is full of or characterized by law, or according to the law.
Think of acting in a way that is full of rules ('law') — that's what 'lawfully' means.