Where does “hepoisenriissat” come from?

hepoisenriissat (Ingrian) comes from Ingrian hepoin, from Proto-Finnic hepoinen, from Proto-Finnic -inen — -ish, -ic, -like, -y; -en.

Ancestry of “hepoisenriissat”, step by step

hepoisenriissat traces back through two separate lines of ancestry.

via Ingrian hepoin

StepLanguageWordMeaning
1Ingrianhepoinhorse
2Proto-Finnichepoinenhorse
3Proto-Finnic-inen-ish, -ic, -like, -y; -en

via Ingrian riista

StepLanguageWordMeaning
1Ingrianriistaobject, thing
Every word from Proto-Finnic -inenEvery word from Proto-Finnic hepoinenEvery word from Ingrian hepoin