Verb

To lie in a position directly beneath.

A stratum of clay underlies the surface gravel.

To lie under or beneath.

To serve as a basis of; form the foundation of.

a doctrine underlying a theory

*{{quote-magazine, year=2013, month=July-August, author= Sarah Glaz

, title= Ode to Prime Numbers , volume=101, issue=4, magazine=(American Scientist) , passage=Some poems, echoing the purpose of early poetic treatises on scientific principles, attempt to elucidate the mathematical concepts that underlie prime numbers. Others play with primes’ cultural associations. Still others derive their structure from mathematical patterns involving primes.}}

To be subject to; be liable to answer, as a charge or challenge.

* Sir Walter Scott

The knight of Ivanhoe underlies the challenge of Brian der Bois Guilbert.

(mining) To underlay.