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.
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            When any country is overlaid by the multitude which
            live upon it.                         --Sir W.
                                                  Raleigh.
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            As when a cloud his beams doth overlay. --Spenser.
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            Framed of cedar overlaid with gold.   --Milton.
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            And overlay
            With this portentous bridge the dark abyss.
                                                  --Milton.
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   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.
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            This woman's child died in the night; because she
            overlaid it.                          --1 Kings iii.
                                                  19.
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            A heap of ashes that o'erlays your fire. --Dryden.
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   4. (Printing) To put an overlay on.
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