IPA: /ˈfɪəsli/
KK: /ˈfɪrslɪ/
In a strong and intense way, often showing great energy or passion.
She fought fiercely to protect her home.
Fiercely → It is formed from "fierce" (from Old French *fier*, meaning proud or fierce) and the suffix "-ly" (meaning in a manner of). The word "fiercely" means in a manner that is fierce or intense.
Think of someone acting in a 'proud' or 'intense' way — 'fierce' describes that strong attitude, and '-ly' shows how they are acting.