Cavy

noun

1. A 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. A rodent of any of several species within the family Caviidae.
3. A living experimental subject.

   "He became a human guinea pig and was paid by the company."

4. A professional company director, without time or real qualifications for the duties.
5. A midshipman in the East India service; (by extension) a low-skilled or non-proficient seaman.