Underlying a. : Lying under or beneath; hence, fundamental; as, the underlying strata of a locality; underlying principles.

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Taxonomy
Merriam-Webster Online Dictionary, Dictionary, webster, Word Games, Webster Online Dictionary with audio pronunciations, thesaurus, adjective, glossary, english, language, ESL, ly, n-d, rock, shale, investigation, inspection, claim.

Defination from the web:
underlying from the Merriam-Webster Online Dictionary with audio pronunciations, thesaurus, Word of the Day, and word games. ... 1 a : lying beneath or below <the underlying rock is shale> b : basic, fundamental <an investigation of the underlying issues> ...