Al vs potash alum

Al and potash alum both are nouns.

Word	Noun	Adjective	Verb	Adverb
Al	Yes	No	No	No
potash alum	Yes	No	No	No

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

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

Other hyponyms of Al include alum, potassium alum, alum, ammonia alum, ammonium alum.

Al (noun)	potash alum (noun)
a silvery ductile metallic element found primarily in bauxite	a white crystalline double sulfate of aluminum: the potassium double sulfate of aluminum