The Collaborative International Dictionary of English v.0.48:

Water monitor \Wa"ter mon"i*tor\ (Zool.)
   A very large lizard (Varanaus salvator) native of India. It
   frequents the borders of streams and swims actively. It
   becomes five or six feet long. Called also two-banded
   monitor, and kabaragoya. The name is also applied to other
   aquatic monitors.
   [1913 Webster]