necessity vs requirement

necessity and requirement both are nouns.

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

As nouns, necessity and requirement are synonyms defined as:

Other synonyms of necessity include essential, necessary, requisite.

necessity (noun)	requirement (noun)
anything indispensable	something that is required in advance
the condition of being essential or indispensable	required activity
	anything indispensable