necessity vs necessary

necessity and necessary both are nouns.

Word	Noun	Adjective	Verb	Adverb
necessity	Yes	No	No	No
necessary	Yes	Yes	No	No

As nouns, necessity and necessary are synonyms defined as:

Other synonyms of necessity include essential, requirement, requisite.

necessity (noun)	necessary (noun)
anything indispensable	anything indispensable
the condition of being essential or indispensable

necessity (adjective)	necessary (adjective)
	absolutely essential
	unavoidably determined by prior circumstances