IPA: /ˈmæn.fəli/
KK: /ˈmæn.fəl.i/
In a way that shows strength, courage, and determination, typically associated with men.
He faced the challenges manfully, never backing down from a fight.
Manfully → It is formed from "man" (from Old English "mann", meaning an adult male human) and "-fully" (meaning in a manner full of or characterized by). The word "manfully" means in a manner characteristic of a man, often implying bravery or strength.
Think of acting 'in a manner full of' ('-fully') the qualities of a 'man' — that's why manfully means to act with courage or strength.