Algae, especially when growing on the surface of a pond. / Worthless, insignificant person or people.

A blowdown valve mounted at the water level of a boiler, used to blow down lighter oily or foamy deposits that float on the water.

plural of scum valve

The buildup of insoluble calcium or magnesium fatty acids from the use of soap with hard water, which leads to a dulling of surfaces and acts as a matrix for trapping soils.

(slang, vulgar, dated) A condom. / (informal, mildly vulgar) A sleazy, disreputable or despicable person; lowlife.

(nonstandard, in Slavic contexts) mackerel

An opaque kind of glaze (layer of paint).

To apply an opaque glaze to an area of a painting to make it softer or duller.

Covered in scum. / (slang) sleazy, worthless, no good

plural of scumbag