scum
nounUK /skʌm/
US /skʌm/
A dirty layer that floats on top of water.
Green scum covered the pond.
OTHER MEANINGS
2. Bad or worthless people.
The police caught the scum who robbed the shop.
3. A layer of waste that forms on a liquid.
Skim the scum off the soup before serving.
4. Impure matter that rises to the top of melted metal.
Workers removed the scum from the molten iron.