nub vs quiddity

nub and quiddity both are nouns.

Word	Noun	Adjective	Verb	Adverb
nub	Yes	No	No	No
quiddity	Yes	No	No	No

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

nub: the choicest or most essential or most vital part of some idea or experience
quiddity: the essence that makes something the kind of thing it is and makes it different from any other

Other hyponyms of nub include bare bones, hypostasis, haecceity, quintessence, stuff.

nub (noun)	quiddity (noun)
the choicest or most essential or most vital part of some idea or experience	the essence that makes something the kind of thing it is and makes it different from any other
a small piece	an evasion of the point of an argument by raising irrelevant distinctions or objections
a small lump or protuberance