scum

Definitions

General English

Construction

  • A deposit, sometimes formed on the surface of clay bricks, caused by soluble salts in the clay that accumulate on the surface during drying, or by the formation of deposits during kiln firing.
  • A mass of organic matter that floats on the surface of sewage.
  • A film of impure matter that forms on the surface of a body of water.

Food

  • The layers of greyish, foamy, coagulated protein and dirt which rise to the top of a simmering liquid. Must be skimmed off or the liquid will lack clarity.

Origin & History of “scum”

Scum is etymologically a ‘layer on top’ of something. The word’s modern connotations of ‘dirt’ are a secondary development. It comes ultimately from prehistoric Germanic *skūman, a derivative of the base *skū- ‘cover’, and its relatives include German schaum ‘foam’ (source of English meerschaum (18th c.), literally ‘sea-foam’). English scum originally meant ‘foam’ too (‘Those small white fish to Venus consecrated, though without Venus’ aid they be created of th’ ocean scum’, Joshua Sylvester, Divine Weeks and Works of Du Bartas 1598), the notion being of a layer of froth ‘covering’ liquid, but by the 15th century it was broadening out to any ‘film on top of liquid’, and from there it went downhill to a ‘film of dirt’ and then simply ‘dirt’. Germanic *skūman was borrowed into Old French as escume, and this formed the basis of a verb escumer ‘remove the top layer’, from which English gets skim (15th c.).
http://www.dictionarycentral.com/definition/scum.html