The Collaborative International Dictionary of English v.0.48:

Cloaca \Clo"a"ca\, n.; pl. Cloac[ae]. [L.]
   1. A sewer; as, the Cloaca Maxima of Rome.
      [1913 Webster]

   2. A privy.
      [1913 Webster]

   3. (Anat.) The common chamber into which the intestinal,
      urinary, and generative canals discharge in birds,
      reptiles, amphibians, and many fishes.
      [1913 Webster]

WordNet (r) 3.0 (2006):

cloaca
    n 1: (zoology) the cavity (in birds, reptiles, amphibians, most
         fish, and monotremes but not mammals) at the end of the
         digestive tract into which the intestinal, genital, and
         urinary tracts open
    2: a waste pipe that carries away sewage or surface water [syn:
       sewer, sewerage, cloaca]