The Collaborative International Dictionary of English v.0.48:

Ferret \Fer"ret\, n. [F. furet, cf. LL. furo; prob. fr. L. fur
   thief (cf. Furtive); cf. Arm. fur wise, sly.] (Zool.)
   An animal of the Weasel family (Mustela furo syn. Putorius
   furo), about fourteen inches in length, of a pale yellow or
   white color, with red eyes. It is a native of Africa, but has
   been domesticated in Europe. Ferrets are used to drive
   rabbits and rats out of their holes. They are sometimes kept
   as pets.
   [1913 Webster +PJC]