underlay (1)

Unlike the root words lay and lie, both verbs are transitive (i.e., take an object). The more common word is underlie, and it has a wider range of meanings including the figurative meaning "be the basis or cause of something": This trend underlies many of the social changes of recent times. The primary meaning of underlay is "to lay something underneath something else" (We underlaid the carpet with felt), and in this meaning it also acts as a noun (with the stress on the first syllable).