Where does “vaahtoontua” come from?

vaahtoontua (Finnish) comes from Finnish vaahto, from Proto-Finnic vakto, from Proto-Germanic þwahtuz, from Proto-Germanic -þuz, from Proto-Indo-European -tus — Derives action nouns from verb roots.

Ancestry of “vaahtoontua”, step by step

StepLanguageWordMeaning
1Finnishvaahtofoam; head; mousse
2Proto-Finnicvaktofoam
3Proto-Germanicþwahtuzwashing, laundry
4Proto-Germanic-þuzForms result nouns from verb roots, usually from...
5Proto-Indo-European-tusDerives action nouns from verb roots
Every word from Proto-Indo-European -tus →Every word from Proto-Germanic -þuz →Every word from Proto-Germanic þwahtuz →