Definition of 'guinea pig'

Noun

1. 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"
      Synonyms: subject case
2. stout-bodied nearly tailless domesticated cavy; often kept as a pet and widely used in research
      Synonyms: Cavia cobaya

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