The Collaborative International Dictionary of English v.0.48:

Scallop \Scal"lop\ (?; 277), n. [OF. escalope a shell, probably
   of German or Dutch origin, and akin to E. scale of a fish;
   cf. D. schelp shell. See Scale of a fish, and cf.
   Escalop.] [Written also scollop.]
   1. (Zool.) Any one of numerous species of marine bivalve
      mollusks of the genus Pecten and allied genera of the
      family Pectinidae. The shell is usually radially ribbed,
      and the edge is therefore often undulated in a
      characteristic manner. The large adductor muscle of some
      the species is much used as food. One species (Vola
      Jacobaeus) occurs on the coast of Palestine, and its
      shell was formerly worn by pilgrims as a mark that they
      had been to the Holy Land. Called also fan shell. See
      Pecten, 2.
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   Note: The common edible scallop of the Eastern United States
         is Pecten irradians; the large sea scallop, also used
         as food, is Pecten Clintonius syn. Pecten
         tenuicostatus.
         [1913 Webster]

   2. One of series of segments of circles joined at their
      extremities, forming a border like the edge or surface of
      a scallop shell.
      [1913 Webster]

   3. One of the shells of a scallop; also, a dish resembling a
      scallop shell.
      [1913 Webster]