The Collaborative International Dictionary of English v.0.48:

Shears \Shears\, n. pl. [Formerly used also in the singular. See
   Shear, n., 1.]
   1. A cutting instrument. Specifically:
      (a) An instrument consisting of two blades, commonly with
          bevel edges, connected by a pivot, and working on both
          sides of the material to be cut, -- used for cutting
          cloth and other substances.
          [1913 Webster]

                Fate urged the shears, and cut the sylph in
                twain.                            --Pope.
          [1913 Webster]
      (b) A similar instrument the blades of which are
          extensions of a curved spring, -- used for shearing
          sheep or skins.
      (c) A shearing machine; a blade, or a set of blades,
          working against a resisting edge.
          [1913 Webster]

   2. Anything in the form of shears. Specifically:
      (a) A pair of wings. [Obs.] --Spenser.
      (b) An apparatus for raising heavy weights, and especially
          for stepping and unstepping the lower masts of ships.
          It consists of two or more spars or pieces of timber,
          fastened together near the top, steadied by a guy or
          guys, and furnished with the necessary tackle.
          [Written also sheers.]
          [1913 Webster]

   3. (Mach.) The bedpiece of a machine tool, upon which a table
      or slide rest is secured; as, the shears of a lathe or
      planer. See Illust. under Lathe.
      [1913 Webster]

   Rotary shears. See under Rotary.
      [1913 Webster]

WordNet (r) 3.0 (2006):

shears
    n 1: large scissors with strong blades