kernel vs nitty-gritty

kernel and nitty-gritty both are nouns.

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

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

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

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

kernel (noun)	nitty-gritty (noun)
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
a single whole grain of a cereal
the inner and usually edible part of a seed or grain or nut or fruit stone