Underlie is defined as to be under, or be the grounds for something.
(verb)See underlie in Webster's New World College Dictionary
transitive verb underlay, underlain, underlying
Origin: ME underlien < OE underlicgan
See underlie in American Heritage Dictionary 4
transitive verb un·der·lay (-lāˈ), un·der·lain (-lānˈ), un·der·ly·ing, un·der·lies
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