The Collaborative International Dictionary of English v.0.48:

Shearbill \Shear"bill`\, n. (Zool.)
   The black skimmer. See Skimmer.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Skimmer \Skim"mer\, n.
   1. One who, or that which, skims; esp., a utensil with which
      liquids are skimmed.
      [1913 Webster]

   2. (Zool.) Any species of longwinged marine birds of the
      genus Rhynchops, allied to the terns, but having the
      lower mandible compressed and much longer than the upper
      one. These birds fly rapidly along the surface of the
      water, with the lower mandible immersed, thus skimming out
      small fishes. The American species (Rhynchops nigra) is
      common on the southern coasts of the United States. Called
      also scissorbill, and shearbill.
      [1913 Webster]

   3. (Zool.) Any one of several large bivalve shells, sometimes
      used for skimming milk, as the sea clams, and large
      scallops.
      [1913 Webster]