rarefaction vs decrease

rarefaction and decrease both are nouns.

Word	Noun	Adjective	Verb	Adverb
rarefaction	Yes	No	No	No
decrease	Yes	No	Yes	No

As nouns, decrease is a hypernym of rarefaction; that is, decrease is a word with a broader meaning than rarefaction:

Other hypernyms of rarefaction include drop-off, lessening.

rarefaction (noun)	decrease (noun)
a decrease in the density of something	the act of decreasing or reducing something
	the amount by which something decreases
	a change downward
	a process of becoming smaller or shorter

rarefaction (verb)	decrease (verb)
	decrease in size, extent, or range
	make become smaller