Source : Webster's Revised Unabridged Dictionary (1913)

Overlay \O`ver*lay"\, v. t. [imp. & p. p. {Overlaid}; p. pr. &
   vb. n. {Overlaying}.]
   1. To lay, or spread, something over or across; hence, to
      cover; to overwhelm; to press excessively upon.

            When any country is overlaid by the multitude which
            live upon it.                         --Sir W.
                                                  Raleigh.

            As when a cloud his beams doth overlay. --Spenser.

            Framed of cedar overlaid with gold.   --Milton.

            And overlay With this portentous bridge the dark
            abyss.                                --Milton.

   2. To smother with a close covering, or by lying upon.

            This woman's child died in the night; because she
            overlaid it.                          --1 Kings iii.
                                                  19.

            A heap of ashes that o'erlays your fire. --Dryden.

   3. (Printing) To put an overlay on.

Source : WordNet®

overlay
     n : protective covering consisting, for example, of a layer of
         boards applied to the studs and joists of a building to
         strengthen it and serve as a foundation for a
         weatherproof exterior [syn: {sheathing}, {overlayer}]
     v 1: put something on top of something else; "cover the meat with
          a lot of gravy" [syn: {cover}]
     2: kill by lying on; "The sow overlay her piglets" [syn: {overlie}]
     [also: {overlaid}]

overlay
     See {overlie}
     [also: {overlaid}]

overlaid
     See {overlay}