The Collaborative International Dictionary of English v.0.48:

Mason \Ma"son\, n. [F. ma[,c]on, LL. macio, machio, mattio,
   mactio, marcio, macerio; of uncertain origin.]
   [1913 Webster]
   1. One whose occupation is to build with stone or brick;
      also, one who prepares stone for building purposes.
      [1913 Webster]

   2. A member of the fraternity of Freemasons. See Freemason.
      [1913 Webster]

   Mason bee (Zool.), any one of numerous species of solitary
      bees of the genus Osmia. They construct curious nests of
      hardened mud and sand.

   Mason moth (Zool.), any moth whose larva constructs an
      earthen cocoon under the soil.

   Mason shell (Zool.), a marine univalve shell of the genus
      Phorus; -- so called because it cements other shells and
      pebbles upon its own shell; a carrier shell.

   Mason wasp (Zool.), any wasp that constructs its nest, or
      brood cells, of hardened mud. The female fills the cells
      with insects or spiders, paralyzed by a sting, and thus
      provides food for its larvae
      [1913 Webster]

WordNet (r) 3.0 (2006):

mason bee
    n 1: any of numerous solitary bees that build nests of hardened
         mud and sand