Definitions
1.nounA tailless rodent of the family Caviidae and the genus Cavia, with short ears and larger than a hamster; the species Cavia porcellus is often kept as a pet.
2.nounA rodent of any of several species within the family Caviidae.
3.nounA living experimental subject."He became a human guinea pig and was paid by the company."
4.nounA professional company director, without time or real qualifications for the duties.
5.nounA midshipman in the East India service; (by extension) a low-skilled or non-proficient seaman.