Skim
Middle English (in the sense ‘remove scum from (a liquid)’): back-formation from skimmer, or from Old French escumer, from escume ‘scum, foam’.
wiktionary
From Middle English skemen, skymen, variants of scumen, from Old French escumer(“to remove scum”), from escume(“froth, foam”), from Frankish *skūm(“froth, foam”), from Proto-Germanic *skūmaz(“foam”), from Proto-Indo-European *skew-(“to cover, conceal”). See scum.
etymonline
skim (v.)
early 15c. (skimmer, the utensil, is attested from late 14c.), "to clear (a liquid) from matter floating on the surface, lift the scum from," from Old French escumer "remove scum," from escume (Modern French écume) "scum," from a Germanic source (compare Old High German scum "scum," German Schaum; see scum). Meaning "to throw (a stone) so as to skip across the surface of (water) is from 1610s. Meaning "to move lightly and rapidly over the surface of" is from 1650s, from the motion involved in skimming liquid; that of "to glance over carelessly" (in reference to printed matter) recorded by 1799. Related: Skimmed; skimming.
