Definition of white rat in English:

white rat

noun

  • An albino rat; (in later use) specifically an albino strain of the brown rat, Rattus norvegicus, bred for use as a laboratory animal or as a pet; a rat of such a strain; also in extended use and figurative.

Origin

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