necessity vs need

necessity and need both are nouns.

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

As nouns, need is a hyponym of necessity; that is, need is a word with a more specific, narrower meaning than necessity:

Other hyponyms of necessity include desideratum, must, want.

As nouns, need is a hypernym of necessity; that is, need is a word with a broader meaning than necessity:

Other hypernyms of necessity include demand.

necessity (noun)	need (noun)
anything indispensable	the psychological feature that arouses an organism to action toward a desired goal; the reason for the action; that which gives purpose and direction to behavior
the condition of being essential or indispensable	anything that is necessary but lacking
	a condition requiring relief
	a state of extreme poverty or destitution

necessity (verb)	need (verb)
	have need of
	have or feel a need for
	require as useful, just, or proper