Webster's Revised Unabridged Dictionary · 1913

(Zoology) 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.

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. [figuratively]

A contemptuous sobriquet. [Obsolete] — Smollett