Pronunciation: (un"dur-lī'), [key]
—v.t. -lay, -lain, -ly•ing.
1. to lie under or beneath; be situated under.
2. to be at the basis of; form the foundation of.
3. Gram.to function as the root morpheme or original or basic form of (a derived form): The form “boy” underlies “boyish.”
4. Finance.to be primary to another right or security.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.