Webster's Revised Unabridged Dictionary · 1913

Underlie

Underlie , transitive verb

[Anglo-Saxon underlicgan. See Under, and Lie to be prostrate.]

1.
To lie under; to rest beneath; to be situated under; as, a stratum of clay underlies the surface gravel.
2.
To be at the basis of; to form the foundation of; to support; as, a doctrine underlying a theory.
3.
To be subject or amenable to. [Rare]
The knight of Ivanhoe... underlies the challenge of Brian der Bois Guilbert. — Sir W. Scott

Underlie , intransitive verb

To lie below or under.

Underlie , noun

See Underlay, n., 1.