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 (cf. 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.
Income not reported for tax purposes, esp from the gross earnings of a gambling casino or other such enterprise; black money: allegedly ''cleansed'' in the neighborhood of $2 million in ''skim,'' untaxed gambling profits/ Caltronics is in on the skim (1960+ Gambling)
: ''appropriate, conceal, and skim'' part of the winnings (1961+ Gambling)