Scum

Part of speech: noun (n.)

1. The extraneous matter or impurities which rise to the surface of liquids in boiling or fermentation, or which form on the surface by other means; also, the scoria of metals in a molten state; dross. Some to remove the scum it did rise. Spenser.

2. refuse; recrement; anything vile or worthless. The great and innocent are insulted by the scum and refuse of the people. Addison.

Part of speech: verb (v.)

1. To take the scum from; to clear off the impure matter from the surface of; to skim. You that scum the molten lead. Dryden & Lee.

2. To sweep or range over the surface of. [Obs.] Wandering up and down without certain seat, they lived by scumming those seas and shores as pirates. Milton.

Part of speech: verb (v.)

To form a scum; to become covered with scum. Also used figuratively. Life, and the interest of life, have stagnated and scummed over. A. K. H. Boyd.