The Collaborative International Dictionary of English v.0.48:

Overlay \O"ver*lay`\, n.
   1. A covering. --Sir W. Scott.
      [1913 Webster]

   2. (Printing) A piece of paper pasted upon the tympan sheet
      to improve the impression by making it stronger at a
      particular place.
      [1913 Webster]

   3. (Computers) A subroutine which occupies a portion of main
      memory which is occupied at some other time by another
      subroutine during execution of the same program. Overlays
      were used as an older technique to allow larger programs
      to be executed in restricted main memory space; the same
      effect is now accomplished by different techniques.
      [PJC]

The Collaborative International Dictionary of English v.0.48:

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.
      [1913 Webster]

            When any country is overlaid by the multitude which
            live upon it.                         --Sir W.
                                                  Raleigh.
      [1913 Webster]

            As when a cloud his beams doth overlay. --Spenser.
      [1913 Webster]

            Framed of cedar overlaid with gold.   --Milton.
      [1913 Webster]

            And overlay
            With this portentous bridge the dark abyss.
                                                  --Milton.
      [1913 Webster]

   2. Specifically: To cover (an object made of an inexpensive
      metal, glass, or other material) with a thin sheet of an
      expensive metal, especially with silver or gold.
      Distinguished from to plate, which is done by a chemical
      or electrical deposition process.
      [PJC]

   3. To smother with a close covering, or by lying upon.
      [1913 Webster]

            This woman's child died in the night; because she
            overlaid it.                          --1 Kings iii.
                                                  19.
      [1913 Webster]

            A heap of ashes that o'erlays your fire. --Dryden.
      [1913 Webster]

   4. (Printing) To put an overlay on.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Overlie \O`ver*lie"\, v. t. [imp. Overlay; p. p. Overlain;
   p. pr. & vb. n. Overlying.]
   To lie over or upon; specifically, to suffocate by lying
   upon; as, to overlie an infant. --Quain.
   [1913 Webster]

         A woman by negligence overlieth her child in her
         sleeping.                                --Chaucer.
   [1913 Webster]

WordNet (r) 3.0 (2006):

overlay
    n 1: 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, overlay, overlayer]
    2: a layer of decorative material (such as gold leaf or wood
       veneer) applied over a surface
    v 1: put something on top of something else; "cover the meat
         with a lot of gravy" [syn: overlay, cover]
    2: kill by lying on; "The sow overlay her piglets" [syn:
       overlie, overlay]

Moby Thesaurus II by Grady Ward, 1.0:

60 Moby Thesaurus words for "overlay":
   adorn, applique, apply to, blanket, block, canopy, cap, cloak,
   clothe, cloud, convolute, cope, cover, cover up, cowl, crown,
   curtain, decorate, eclipse, elaborate, embellish, embroider,
   enrich, festoon, film, flap, flourish, fly, gild, hood,
   imbrication, involve, lap, lay on, lay over, load with ornament,
   mantle, mask, muffle, obduce, obscure, occult, ornament, overcast,
   overcharge, overlap, overlapping, overlayer, overload, overspread,
   put on, screen, scum, shield, spread over, superimpose, superpose,
   trick out, varnish, veil