from
The Collaborative International Dictionary of English v.0.48
Guinea pig \Guin"ea 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]