amortization vs diminution

amortization and diminution both are nouns.

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

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

amortization: the reduction of the value of an asset by prorating its cost over a period of years
diminution: the act of decreasing or reducing something

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

amortization (noun)	diminution (noun)
payment of an obligation in a series of installments or transfers	the act of decreasing or reducing something
the reduction of the value of an asset by prorating its cost over a period of years	the statement of a theme in notes of lesser duration (usually half the length of the original)
	change toward something smaller or lower