In the original texts, unicorns go by the Hebrew name Re-em whereas the Greek Septuagint used the name Monokeros. Unicorn itself is Latin. All three names mean "one horn".
While popularly characterized as a horned member of the horse baramin, it is likely that the unicorn was actually quite unhorselike. One recognized theory is that the unicorn was actually the rhinoceros, however a growing number of Creation researchers are theorizing that the unicorn was actually a member of the ceratopsian baramin.
Post-Noachian references to unicorns have led some researchers to argue that unicorns are still alive today. At the very least, it is likely that they were taken aboard the Ark prior to the Great Flood.