IPA: /ˈmɑːrvələsli/
KK: /ˈmɑrvələsli/
In a way that is wonderful or amazing.
She performed marvelously in the competition, impressing everyone with her skills.
Marvelously → It is formed from "marvel" (from Old French *merveille*, meaning wonder or surprise) and "-ously" (meaning in a manner characterized by). The word "marvelously" means in a manner that is full of wonder or amazement.
Think of something that is full of 'wonder' ('marvel') and done 'in a manner' ('-ously') that amazes you.