A vaccination pen is a device used for administering vaccines to livestock. However, there are a few synonyms that can be used to describe the same device. One alternative term could be an injection gun, which is a tool that pulls a vaccine from a container and pushes it into the animal's skin. Another synonym for a vaccination pen is a vaccinator, which is a device that is inserted into the animal's skin to deliver the vaccine. Additionally, a needle-free injector can also be considered a synonym, as it releases the vaccine into the animal's skin through a high-pressure stream of fluid, rather than using a needle. Overall, these terms can be used interchangeably to describe a device that delivers vaccines to animals efficiently and safely.