The Collaborative International Dictionary of English v.0.48:

Quaker \Quak"er\, n.
   1. One who quakes.
      [1913 Webster]

   2. One of a religious sect founded by George Fox, of
      Leicestershire, England, about 1650, -- the members of
      which call themselves Friends. They were called Quakers,
      originally, in derision. See Friend, n., 4.
      [1913 Webster]

            Fox's teaching was primarily a preaching of
            repentance . . . The trembling among the listening
            crowd caused or confirmed the name of Quakers given
            to the body; men and women sometimes fell down and
            lay struggling as if for life.        --Encyc. Brit.
      [1913 Webster]

   3. (Zool.)
      (a) The nankeen bird.
      (b) The sooty albatross.
      (c) Any grasshopper or locust of the genus Edipoda; --
          so called from the quaking noise made during flight.
          [1913 Webster]

   Quaker buttons. (Bot.) See Nux vomica.

   Quaker gun, a dummy cannon made of wood or other material;
      -- so called because the sect of Friends, or Quakers, hold
      to the doctrine, of nonresistance.

   Quaker ladies (Bot.), a low American biennial plant
      (Houstonia c[ae]rulea), with pretty four-lobed corollas
      which are pale blue with a yellowish center; -- also
      called bluets, and little innocents.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Quaker gun
    n 1: a dummy gun or piece of artillery made usually of wood