necessary vs need

necessary and need both are nouns.

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

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

Other hyponyms of necessary include desideratum, must, want.

necessary (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
	anything that is necessary but lacking
	a condition requiring relief
	a state of extreme poverty or destitution

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

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