necessary vs must

necessary and must both are nouns.

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

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

Other hyponyms of necessary include desideratum, need, want.

necessary (noun)	must (noun)
anything indispensable	the quality of smelling or tasting old or stale or mouldy
	grape juice before or during fermentation
	a necessary or essential thing

necessary (adjective)	must (adjective)
absolutely essential	highly recommended
unavoidably determined by prior circumstances