erosion vs diminution

erosion and diminution both are nouns.

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

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

Other hypernyms of erosion include decline.

erosion (noun)	diminution (noun)
(geology) the mechanical process of wearing or grinding something down (as by particles washing over it), also figuratively	the act of decreasing or reducing something
erosion by chemical action	the statement of a theme in notes of lesser duration (usually half the length of the original)
a gradual decline of something	change toward something smaller or lower
condition in which the earth's surface is worn away by the action of water and wind