Definition of water lizard in US English:

water lizard

noun

  • (Originally) any of various lizards or lizard-like animals living in or near water, especially a newt (family Salamandridae) (now rare); (in later use) specifically a monitor lizard (family Varanidae), especially one that is a strong swimmer.

Origin

Early 17th century; earliest use found in Edward Topsell (d. 1625), Church of England clergyman and author.