necessity vs urgency

necessity and urgency both are nouns.

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

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

Other hyponyms of necessity include requisiteness, exigency.

necessity (noun)	urgency (noun)
anything indispensable	pressing importance requiring speedy action
the condition of being essential or indispensable	insistent solicitation and entreaty
	the state of being urgent; an earnest and insistent necessity
	an urgent situation calling for prompt action