shrinkage vs lessening

shrinkage and lessening both are nouns.

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

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

Other hypernyms of shrinkage include decrease, drop-off.

shrinkage (noun)	lessening (noun)
the act of stealing goods that are on display in a store	a change downward
the amount by which something shrinks
process or result of becoming less or smaller