The Collaborative International Dictionary of English v.0.48:

Sorb \Sorb\, n.[L. sorbus the tree, sorbum the fruit; cf. F.
   sorbe. See Service tree.] (Bot.)
   (a) The wild service tree (Pyrus torminalis) of Europe;
       also, the rowan tree.
   (b) The fruit of these trees.
       [1913 Webster]

   Sorb apple, the fruit of the sorb, or wild service tree.

   Sorb tree, the wild service tree.
      [1913 Webster]

WordNet (r) 3.0 (2006):

sorb apple
    n 1: medium-sized European tree resembling the rowan but bearing
         edible fruit [syn: service tree, sorb apple, sorb
         apple tree, Sorbus domestica]
    2: acid gritty-textured fruit [syn: sorb, sorb apple]