/ ˌʌndəˈlaɪ; NAmE ˌʌndərˈlaɪ/ verb
( under·lying , under·lay / -ˈleɪ; NAmE / under·lain / -ˈleɪn; NAmE /) [ vn ] [ no passive ] ( formal ) to be the basis or cause of sth :
These ideas underlie much of his work.
It is a principle that underlies all the party's policies.
—see also underlying
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WORD ORIGIN
Old English underlicgan be subject or subordinate to (from under- , lie (I)).