scum scum /ˈskʌm/

noun

1. A film of impurities or vegetation that can form on the surface of a liquid  ( scum )
   a film of impurities or vegetation that can form on the surface of a liquid
   
2. [Informal] Worthless people  ( scum [Informal] , trash [Informal, N. American] )
   worthless people
   

verb

1. Remove the scum from  ( scum )
   remove the scum from