Where does “scum” come from?

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

Ancestry of “scum”, step by step

StepLanguageWordMeaning
1Old Dutchskūm—
2Frankishskūmfoam; froth, foam
3Proto-Germanicskūmazfilm; grime; scum; foam; froth; yeast
4Proto-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 →
scum — Etymology, Origin & Word History | Etymology Explorer