lessening vs alteration

lessening and alteration both are nouns.

Word	Noun	Adjective	Verb	Adverb
lessening	Yes	No	No	No
alteration	Yes	No	No	No

As nouns, alteration is a hypernym of lessening; that is, alteration is a word with a broader meaning than lessening:

lessening: a change downward
alteration: an event that occurs when something passes from one state or phase to another

Other hypernyms of lessening include change, modification.

lessening (noun)	alteration (noun)
a change downward	the act of revising or altering (involving reconsideration and modification)
	the act of making something different (as e.g. the size of a garment)
	an event that occurs when something passes from one state or phase to another