Where does “Bilous” come from?

Bilous (English) comes from Ukrainian Білоус, from Proto-Slavic *běloǫsъ, from Proto-Slavic bělъ, from Proto-Indo-European bʰēlHs — white surface or stain.

Ancestry of “Bilous”, step by step

StepLanguageWordMeaning
1UkrainianБілоус—
2Proto-Slavic*běloǫsъwhite-moustached, whitebeard
3Proto-Slavicbělъwhite
4Proto-Indo-EuropeanbʰēlHswhite surface or stain
Every word from Proto-Indo-European bʰēlHs →Every word from Proto-Slavic bělъ →Every word from Proto-Slavic *běloǫsъ →