aluminum vs alum

aluminum and alum both are nouns.

Word	Noun	Adjective	Verb	Adverb
aluminum	Yes	No	No	No
alum	Yes	No	No	No

As nouns, alum is a hyponym of aluminum; that is, alum is a word with a more specific, narrower meaning than aluminum:

aluminum: a silvery ductile metallic element found primarily in bauxite
alum: a white crystalline double sulfate of aluminum: the potassium double sulfate of aluminum

Other hyponyms of aluminum include potash alum, potassium alum, ammonia alum, ammonium alum.

aluminum (noun)	alum (noun)
a silvery ductile metallic element found primarily in bauxite	a double sulphate of aluminum and potassium that is used as an astringent (among other things)
	a white crystalline double sulfate of aluminum: the potassium double sulfate of aluminum
	a white crystalline double sulfate of aluminum: the ammonium double sulfate of aluminum
	a person who has received a degree from a school (high school or college or university)