Manfully means with determined courage. Struggle manfully, manfully resisted, carry on manfully.
It is dated and often faintly comic now — manfully usually describes somebody making a brave show of a losing effort. The assumption buried in it, that courage is male, is why writers reach for gamely or bravely instead.
1adverbmanfullyWith determined courage.
“Though his team was losing badly, the goalkeeper struggled on manfully until the final whistle.”
manfully is a manner.
Manful plus -ly, from man plus -ful. The word assumes courage as a male quality, which is why it has dated.
Middle English
manfully
English, today
manfully
From Middle English manfully; equivalent to manful + ly.
Etymology from Wiktionary, CC BY-SA