meat and potatoes vs groundwork

meat and potatoes and groundwork both are nouns.

Word	Noun	Adjective	Verb	Adverb
meat and potatoes	Yes	No	No	No
groundwork	Yes	No	No	No

As nouns, groundwork is a hypernym of meat and potatoes; that is, groundwork is a word with a broader meaning than meat and potatoes:

meat and potatoes: the fundamental part
groundwork: the fundamental assumptions from which something is begun or developed or calculated or explained

Other hypernyms of meat and potatoes include base, basis, cornerstone, foundation, fundament.

meat and potatoes (noun)	groundwork (noun)
the fundamental part	preliminary preparation as a basis or foundation
	lowest support of a structure
	the fundamental assumptions from which something is begun or developed or calculated or explained