nitty-gritty vs marrow

nitty-gritty and marrow both are nouns.

Word	Noun	Adjective	Verb	Adverb
nitty-gritty	Yes	No	No	No
marrow	Yes	No	No	No

As nouns, nitty-gritty and marrow are synonyms defined as:

nitty-gritty and marrow: the choicest or most essential or most vital part of some idea or experience

Other synonyms of nitty-gritty include center, centre, core, essence, gist, heart, heart and soul, inwardness, kernel, meat, nub, pith, substance, sum.

nitty-gritty (noun)	marrow (noun)
the choicest or most essential or most vital part of some idea or experience	the fatty network of connective tissue that fills the cavities of bones
	the choicest or most essential or most vital part of some idea or experience
	large elongated squash with creamy to deep green skins
	very tender and very nutritious tissue from marrowbones
	any of various squash plants grown for their elongated fruit with smooth dark green skin and whitish flesh