quiddity vs heart and soul

quiddity and heart and soul both are nouns.

Word	Noun	Adjective	Verb	Adverb
quiddity	Yes	No	No	No
heart and soul	Yes	No	No	Yes

As nouns, heart and soul is a hypernym of quiddity; that is, heart and soul is a word with a broader meaning than quiddity:

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

Other hypernyms of quiddity include center, centre, core, essence, gist, heart, inwardness, kernel, marrow, meat, nitty-gritty, nub, pith, substance, sum.

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

quiddity (adverb)	heart and soul (adverb)
	with complete faith