It’s unclear why guinea pigs have been given such a name, but many people think that ‘pig’ is due to their shape and mannerisms. They are round and stout with blunt heads, and walk in a similar fashion to actual pigs. This may have led people to believe them related, but in actual fact, guinea pigs aren’t members of the pig family but of the rodent family, which consists of animals such as hamsters and rats.
The term 'guinea pig' is probably due to a misconception
Another misconception surrounds the term ‘guinea’ - some people mistakenly believe that ‘guinea’ is a relic of the monetary worth of these animals in days gone by, and that their price has stuck with them long since guineas have fallen out of use. Although this is a fun anecdote it’s unlikely to be true, as guinea pigs were known as such long before guineas were used as currency. It’s quite likely that the ‘guinea’ section of the name is actually a mistake, and is some reference to the idea that the animals were brought to Europe from Guinea, when at most they stayed there temporarily on their voyage from South America.