The Collaborative International Dictionary of English v.0.48:

Cavy \Ca"vy\, n.; pl. Cavies. [NL. cavia, fr. Brazilian
   cabiai: cf. F. cabiai.] (Zool.)
   A rodent of the genera Cavia and Dolichotis, as the
   guinea pig (Cavia cobaya). Cavies are natives of South
   America.
   [1913 Webster]

   Water cavy (Zool.), The capybara.
      [1913 Webster]