bare bones vs nitty-gritty

bare bones and nitty-gritty both are nouns.

Word	Noun	Adjective	Verb	Adverb
bare bones	Yes	No	No	No
nitty-gritty	Yes	No	No	No

As nouns, nitty-gritty is a hypernym of bare bones; that is, nitty-gritty is a word with a broader meaning than bare bones:

bare bones: (plural) the most basic facts or elements
nitty-gritty: the choicest or most essential or most vital part of some idea or experience

Other hypernyms of bare bones include center, centre, core, essence, gist, heart, heart and soul, inwardness, kernel, marrow, meat, nub, pith, substance, sum.

bare bones (noun)	nitty-gritty (noun)
(plural) the most basic facts or elements	the choicest or most essential or most vital part of some idea or experience