The Collaborative International Dictionary of English v.0.48:

Washer \Wash"er\, n. [AS. w[ae]scere.]
   1. One who, or that which, washes.
      [1913 Webster]

   2. A ring of metal, leather, or other material, or a
      perforated plate, used for various purposes, as around a
      bolt or screw to form a seat for the head or nut, or
      around a wagon axle to prevent endwise motion of the hub
      of the wheel and relieve friction, or in a joint to form a
      packing, etc.
      [1913 Webster]

   3. (Plumbing) A fitting, usually having a plug, applied to a
      cistern, tub, sink, or the like, and forming the outlet
      opening.
      [1913 Webster]

   4. (Zool.) The common raccoon.
      [1913 Webster]

   5. (Zool.) Same as Washerwoman, 2. [Prov. Eng.]
      [1913 Webster]

WordNet (r) 3.0 (2006):

washer
    n 1: someone who washes things for a living
    2: seal consisting of a flat disk placed to prevent leakage
    3: a home appliance for washing clothes and linens automatically
       [syn: washer, automatic washer, washing machine]