The Collaborative International Dictionary of English v.0.48:

Mosaic \Mo*sa"ic\, n. [F. mosa["i]que; cf. Pr. mozaic, musec,
   Sp. & Pg. mosaico, It. mosaico, musaico, LGr. ?, ?, L.
   musivum; all fr. Gr. ? belonging to the Muses. See Muse the
   goddess.]
   1. (Fine Arts) A surface decoration made by inlaying in
      patterns small pieces of variously colored glass, stone,
      or other material; -- called also mosaic work.
      [1913 Webster]

   2. A picture or design made in mosaic; an article decorated
      in mosaic.
      [1913 Webster]

   3. Something resembling a mosaic[1]; something made up of
      different pieces, fitted together by design to form a
      unified composition.
      [PJC]

   aerial mosaic An aerial photograph of a large area, made by
      carefully fitting together aerial photographs of smaller
      areas so that the edges match in location, and the whole
      provides a continuous image of the larger area. Called
      also

   mosaic map and photomosaic.

   mosaic virus A type of plant virus that causes green and
      yellow mottling of leaves of a plant. A much-studied type
      is the tobacco mosaic virus, affecting the tobacco
      plant.
      [PJC]

WordNet (r) 3.0 (2006):

tobacco mosaic virus
    n 1: the widely studied plant virus that causes tobacco mosaic;
         it was the first virus discovered (1892) [syn: tobacco
         mosaic virus, TMV]