The Collaborative International Dictionary of English v.0.48:

Dishwater \Dish"wa`ter\, n.
   Water in which dishes have been washed. "Suds and dishwater."
   --Beau. & Fl.
   [1913 Webster]

WordNet (r) 3.0 (2006):

dishwater
    n 1: water in which dishes and cooking utensils are washed

Moby Thesaurus II by Grady Ward, 1.0:

63 Moby Thesaurus words for "dishwater":
   bilge, bilgewater, bones, cambric tea, carrion, chaff, cobweb,
   culm, deadwood, ditchwater, draff, dregs, dust, filings, garbage,
   gash, gossamer, gruel, hair, hogwash, house of cards, husks,
   leavings, lees, matchwood, milk and water, offal, offscourings,
   orts, parings, potsherds, rags, raspings, reed, refuse, riffraff,
   rope of sand, sand castle, scourings, scrap iron, scraps, scum,
   scurf, sewage, sewerage, shards, shavings, slack, slag, slop,
   slops, slough, stubble, sweepings, swill, tares, thread, wastage,
   waste, waste matter, wastepaper, water, weeds