The Collaborative International Dictionary of English v.0.48:

Washerwoman \Wash"er*wom`an\, n.; pl. Washerwomen.
   [1913 Webster]
   1. A woman who washes clothes, especially for hire, or for
      others.
      [1913 Webster]

   2. (Zool.) The pied wagtail; -- so called in allusion to its
      beating the water with its tail while tripping along the
      leaves of water plants. [Prov. Eng.]
      [1913 Webster]

WordNet (r) 3.0 (2006):

washerwoman
    n 1: a working woman who takes in washing [syn: washwoman,
         washerwoman, laundrywoman, laundress]