tighten vs contract

tighten is not a noun while contract is a noun.

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

As verbs, contract is a hyponym of tighten; that is, contract is a word with a more specific, narrower meaning than tighten:

Other hyponyms of tighten include constrict, constringe, narrow, firm, tauten, compact, compress, constrict, press, squeeze, strain, tense.

tighten (noun)	contract (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

tighten (verb)	contract (verb)
become tight or tighter	be stricken by an illness, fall victim to an illness
make tight or tighter	make or become more narrow or restricted
severely restrict in scope or extent	become smaller or draw together
narrow or limit	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