tightening vs alteration

tightening and alteration both are nouns.

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

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

tightening: the act of making something tighter
alteration: the act of making something different (as e.g. the size of a garment)

Other hypernyms of tightening include adjustment, modification.

tightening (noun)	alteration (noun)
the act of making something tighter	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