guinea pig

The origin of "guinea" in "guinea pig" is uncertain. One theory is that the animals, which are originally from South America, were brought to Europe by way of Guinea, leading people to think they had originated there. "Guinea" was also frequently used in English to refer generally to any far-off, unknown country, and so the name may simply be a colorful reference to the animal's foreignness. Others believe "guinea" may be an alteration of the word coney (“rabbit”); guinea pigs were referred to as "pig coneys" in Edward Topsell's 1607 treatise on quadrupeds.

The figurative sense of "experimental subject" was first used in the early 20th century, according to the Oxford English Dictionary, which cites examples from 1913 and 1920. It arose from the once extensive usage of guinea pigs in scientific research since at least the 17th century, which had a peak in popularity in the 19th and 20th centuries, when they were part of groundbreaking germ-theory research and of orbital space flights. Compare Italian cavia, Portuguese cobaia, and the latter's loans into French cobaye, Spanish cobaya, Romanian cobai, and Turkish kobay, all of which mean both "guinea pig" and "volunteer for lab experiment", with the latter often being the commoner sense.