marrow vs nitty-gritty

marrow and nitty-gritty both are nouns.

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

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

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

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

marrow (noun)	nitty-gritty (noun)
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
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