amortisation vs step-down

amortisation and step-down both are nouns.

Word	Noun	Adjective	Verb	Adverb
amortisation	Yes	No	No	No
step-down	Yes	No	No	No

As nouns, step-down is a hypernym of amortisation; that is, step-down is a word with a broader meaning than amortisation:

amortisation: the reduction of the value of an asset by prorating its cost over a period of years
step-down: the act of decreasing or reducing something

Other hypernyms of amortisation include decrease, diminution, reduction.

amortisation (noun)	step-down (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