slag vs scum

slag and scum both are nouns.

Word	Noun	Adjective	Verb	Adverb
slag	Yes	No	Yes	No
scum	Yes	No	Yes	No

As nouns, scum is a hypernym of slag; that is, scum is a word with a broader meaning than slag:

slag: the scum formed by oxidation at the surface of molten metals
scum: a film of impurities or vegetation that can form on the surface of a liquid

slag (noun)	scum (noun)
the scum formed by oxidation at the surface of molten metals	a film of impurities or vegetation that can form on the surface of a liquid
	worthless people

slag (verb)	scum (verb)
convert into slag	remove the scum from