verb (used with object), un·der·lay, un·der·lain, un·der·ly·ing.
- to lie under or beneath; be situated under.
- to be at the basis of; form the foundation of.
- Grammar. to function as the root morpheme or original or basic form of (a derived form): The form “boy” underlies “boyish.”
- Finance. to be primary to another right or security.
verb -lies, -lying, -lay or -lain (tr)
- to lie or be placed under or beneath
- to be the foundation, cause, or basis ofcareful planning underlies all our decisions
- finance to take priority over (another claim, liability, mortgage, etc)a first mortgage underlies a second
- to be the root or stem from which (a word) is derived“happy” underlies “happiest”
v.Old English under licgan “to be subordinate to, to submit to;” see under + lie (v.2). Meaning “to lie under or beneath” is attested from c.1600; figurative sense of “to be the basis of” is attested from 1852 (implied in underlying).