Guinea pig

[ Prob. a mistake for Guiana pig. ] 1. (Zool.) A small Brazilian rodent (Cavia porcellus or Cavia cobaya), about seven inches in length and usually of a white color, with spots of orange and black. Called also cavy. It is the domesticated form of the wild cavy, often kept as a pet and used commonly as an experimental animal in laboratory research. [ Webster 1913 Suppl. +PJC ]

2. Hence, [ figuratively ]: Any animal or person used in an experiment; -- also applied to people who are unwillingly or unknowingly subjected by authorities to policies or procedures which might cause bodily or mental harm. [ PJC ]

3. A contemptuous sobriquet. [ Obs. ] Smollett [ Webster 1913 Suppl. +PJC ]