adjustment vs loosening

adjustment and loosening both are nouns.

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

As nouns, loosening is a hyponym of adjustment; that is, loosening is a word with a more specific, narrower meaning than adjustment:

adjustment: the act of making something different (as e.g. the size of a garment)
loosening: the act of making something less tight

Other hyponyms of adjustment include laxation, tightening, accommodation, adaptation, tune.

adjustment (noun)	loosening (noun)
the act of making something different (as e.g. the size of a garment)	the act of making something less tight
the act of adjusting something to match a standard	an occurrence of control or strength weakening
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)