Where does “skum” come from?

skum (Middle English) comes from Middle Dutch schūme, from Old Dutch *scūm, from Frankish skūm, from Proto-Germanic skūmaz, from Proto-Indo-European (s)kewH- — to cover, bedeck; cover.

Ancestry of “skum”, step by step

StepLanguageWordMeaning
1Middle Dutchschūmefoam
2Old Dutch*scūm—
3Frankishskūmfoam; froth, foam
4Proto-Germanicskūmazfilm; grime; scum; foam; froth; yeast
5Proto-Indo-European(s)kewH-to cover, bedeck; cover
Every word from Proto-Indo-European (s)kewH- →Every word from Proto-Germanic skūmaz →Every word from Frankish skūm →