Rihannsu is a fictional language invented by author Diane Duane which is spoken by the Rihannsu (Romulans) in Duane's Star Trek novels. In her novel The Romulan Way (ISBN 0-7434-0370-3), as the inhabitants of the planet Vulcan turn to the philosophy of Surak en masse, the followers of S'task decide that they can no longer remain on Vulcan. As part of their exodus, they intentionally invent a new culture and a new language, based on Old High Vulcan and "aged" in a different direction. This language, described as sounding somewhat like Latin and Welsh, came to be known as Rihannsu.