alleviation vs diminution

alleviation and diminution both are nouns.

Word	Noun	Adjective	Verb	Adverb
alleviation	Yes	No	No	No
diminution	Yes	No	No	No

As nouns, diminution is a hypernym of alleviation; that is, diminution is a word with a broader meaning than alleviation:

alleviation: the act of reducing something unpleasant (as pain or annoyance)
diminution: the act of decreasing or reducing something

Other hypernyms of alleviation include decrease, reduction, step-down.

alleviation (noun)	diminution (noun)
the act of reducing something unpleasant (as pain or annoyance)	the act of decreasing or reducing something
the feeling that comes when something burdensome is removed or reduced	the statement of a theme in notes of lesser duration (usually half the length of the original)
	change toward something smaller or lower