Where does “fiers” come from?

fiers (Middle English) comes from Old French fers, from Latin ferus, from Proto-Indo-European ǵʰwer- — wild; wild animal.

Ancestry of “fiers”, step by step

Step	Language	Word	Meaning
1	Old French	fers	wild", "ferocious
2	Latin	ferus	wild, savage; uncivilized, uncultivated; untamed,...
3	Proto-Indo-European	ǵʰwer-	wild; wild animal

fiers — Etymology, Origin & Word History | Etymology Explorer