/ Dictionary / Index U underlie: Meaning and Definition of Find definitions for: un•der•lie Pronunciation: (un"dur-lī'), [key] — -lay, -lain, -ly•ing. to lie under or beneath; be situated under. to be at the basis of; form the foundation of. to function as the root morpheme or original or basic form of (a derived form): The form “boy” underlies “boyish.” to be primary to another right or security. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: underlie (Thesaurus) underlet underline Related Content Daily Word Quiz: serendipity Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language