diminish vs decrease

diminish is not a noun while decrease is a noun.

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

As verbs, diminish and decrease are synonyms defined as:

Other synonyms of diminish include fall, lessen.

As verbs, decrease is a hypernym of diminish; that is, decrease is a word with a broader meaning than diminish:

Other hypernyms of diminish include lessen, minify.

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

diminish (verb)	decrease (verb)
decrease in size, extent, or range	decrease in size, extent, or range
lessen the authority, dignity, or reputation of	make become smaller