groundwork vs substructure

groundwork and substructure both are nouns.

Word	Noun	Adjective	Verb	Adverb
groundwork	Yes	No	No	No
substructure	Yes	No	No	No

As nouns, groundwork and substructure are synonyms defined as:

Other synonyms of groundwork include base, foot, foundation, fundament, understructure.

groundwork (noun)	substructure (noun)
preliminary preparation as a basis or foundation	lowest support of a structure
lowest support of a structure	the basic structure or features of a system or organization
the fundamental assumptions from which something is begun or developed or calculated or explained