contract vs lessen

contract is a noun but lessen is not a noun.

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

As verbs, lessen is a hypernym of contract; that is, lessen is a word with a broader meaning than contract:

Other hypernyms of contract include decrease, diminish, fall.

As verbs, lessen is a hypernym of contract; that is, lessen is a word with a broader meaning than contract:

Other hypernyms of contract include decrease, minify.

contract (noun)	lessen (noun)
a variety of bridge in which the bidder receives points toward game only for the number of tricks he bid
a binding agreement between two or more persons that is enforceable by law
(contract bridge) the highest bid becomes the contract setting the number of tricks that the bidder must make

contract (verb)	lessen (verb)
be stricken by an illness, fall victim to an illness	decrease in size, extent, or range
make or become more narrow or restricted	wear off or die down
become smaller or draw together	make become smaller
reduce in scope while retaining essential elements
compress or concentrate
enter into a contractual arrangement
make smaller
squeeze or press together
engage by written agreement