underlay (Noun) — A pad placed under a carpet.
underlay (Verb) — (printing) raise or support (the level of printing) by inserting a piece of paper or cardboard under the type. ex. "underlay the plate"
underlay (Verb) — Put (something) under or beneath. ex. "They underlaid the shingles with roofing paper"
underlay (Verb) — Provide with a base, support, lining, or backing. ex. "underlay the boards with joists"
underlay (Verb) — Be or form the base for.
underlay (Verb) — Lie underneath.