first principles vs bedrock

first principles and bedrock both are nouns.

Word	Noun	Adjective	Verb	Adverb
first principles	Yes	No	No	No
bedrock	Yes	No	No	No

As nouns, bedrock is a hypernym of first principles; that is, bedrock is a word with a broader meaning than first principles:

Other hypernyms of first principles include basic principle, basics, fundamental principle, fundamentals.

first principles (noun)	bedrock (noun)
the elementary stages of any subject (usually plural)	principles from which other truths can be derived
	solid unweathered rock lying beneath surface deposits of soil