Scum, v. t. [imp. & p. p.Scummed (?); p. pr. & vb. n.Scumming (?).] 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.
Wandering up and down without certain seat, they lived by scumming those seas and shores as pirates. Milton.