desideratum vs necessity

desideratum and necessity both are nouns.

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

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

Other hypernyms of desideratum include essential, necessary, requirement, requisite.

desideratum (noun)	necessity (noun)
something desired as a necessity	anything indispensable
	the condition of being essential or indispensable