tightening vs adjustment

tightening and adjustment both are nouns.

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

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

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

Other hypernyms of tightening include alteration, modification.

tightening (noun)	adjustment (noun)
the act of making something tighter	the act of making something different (as e.g. the size of a garment)
	the act of adjusting something to match a standard
	making or becoming suitable; adjusting to circumstances
	an amount added or deducted on the basis of qualifying circumstances
	the process of adapting to something (such as environmental conditions)