Noun guinea pig has 2 senses
  1. subject, case, guinea pig - a person who is subjected to experimental or other observational procedures; someone who is an object of investigation; "the subjects for this investigation were selected randomly"; "the cases that we studied were drawn from two different communities"
    --1 is a kind of person, individual, someone, somebody, mortal, human, soul
  2. guinea pig, Cavia cobaya - stout-bodied nearly tailless domesticated cavy; often kept as a pet and widely used in research
    --2 is a kind of cavy