scum
noun /skʌm/
  /skʌm/
- [uncountable, singular] a layer of bubbles or an unpleasant substance that forms on the surface of a liquid
- Skim off any scum.
 - stinking water covered by a thick green scum
 
 - [uncountable, plural] (informal) an offensive word for people who you think are very bad
- Don't waste your sympathy on scum like that.
 - Drug dealers are the scum of the earth (= the worst people there are).
 
 
Word OriginMiddle English: from Middle Low German, Middle Dutch schūm, of Germanic origin.