Where does “eväs” come from?

eväs (Proto-Finnic) comes from Proto-Indo-European yéwos, from Proto-Indo-European yew- — to mix.

Ancestry of “eväs”, step by step

Step	Language	Word	Meaning
1	Proto-Indo-European	yéwos	cereal, grain; barley, spelt
2	Proto-Indo-European	yew-	to mix

eväs — Etymology, Origin & Word History | Etymology Explorer