D defs.my
Entry 3 senses Webster, 1913

Guinea pig

· Guin·ea pig · IPA /ˈɡɪni pɪɡ/
01 A small Brazilian rodent (Cavia porcellus or Cavia cobaya), about seven inches in length and usually of a white color, with spots of orange…
  1. 1.
    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.(Zool.) Also: cavy
  2. 2.
    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]
  3. 3.
    A contemptuous sobriquet.[Obs.]