Where does “Mastny” come from?

Mastny (English) comes from Czech mastný, from Czech mast, from Old Czech mast, from Proto-Slavic mastь, from Proto-Slavic -tь, from Proto-Indo-European -tis — Derives abstract/action nouns from verb roots.

Ancestry of “Mastny”, step by step

StepLanguageWordMeaning
1Czechmastnýgreasy; expensive
2Czechmastointment
3Old Czechmastointment
4Proto-Slavicmastьointment
5Proto-Slavic-tьDeverbative, creates nouns denoting act, state,...
6Proto-Indo-European-tisDerives abstract/action nouns from verb roots
Every word from Proto-Indo-European -tis →Every word from Proto-Slavic -tь →Every word from Proto-Slavic mastь →