essential vs necessity

essential and necessity both are nouns.

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

As nouns, essential and necessity are synonyms defined as:

Other synonyms of essential include necessary, requirement, requisite.

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

essential (adjective)	necessity (adjective)
basic and fundamental
defining rights and duties as opposed to giving the rules by which rights and duties are established
being or relating to or containing the essence of a plant etc
of the greatest importance
absolutely necessary; vitally necessary