underlying vs rudimentary

underlying and rudimentary both are adjectives.

Word	Noun	Adjective	Verb	Adverb
underlying	No	Yes	No	No
rudimentary	No	Yes	No	No

As adjectives, underlying and rudimentary are synonyms defined as:

underlying and rudimentary: being or involving basic facts or principles

Other synonyms of underlying include fundamental.

underlying (adjective)	rudimentary (adjective)
being or involving basic facts or principles	being or involving basic facts or principles
in the nature of something though not readily apparent	being in the earliest stages of development
located beneath or below	not fully developed in mature animals