decrease vs lessen

decrease is a noun but lessen is not a noun.

Word	Noun	Adjective	Verb	Adverb
decrease	Yes	No	Yes	No
lessen	No	No	Yes	No

As verbs, decrease and lessen are synonyms defined as:

Other synonyms of decrease include diminish, fall.

As verbs, decrease and lessen are synonyms defined as:

Other synonyms of decrease include minify.

decrease (noun)	lessen (noun)
the act of decreasing or reducing something
the amount by which something decreases
a change downward
a process of becoming smaller or shorter

decrease (verb)	lessen (verb)
decrease in size, extent, or range	decrease in size, extent, or range
make become smaller	wear off or die down
	make become smaller