The most common prefix for the number nine is "nona-", such as in the word "nonagon," which describes a polygon with nine sides, and "nonagenarian," a person in his 90s. A less commonly used prefix is "nove-," as in "novennial," which is an event that occurs every nine years.
Another prefix used for the number nine is "novem-," as in the month "November," which used to be the ninth month in the ancient Roman calendar. Another prefix is "ennea-," which is derived from Greek and used in the word "enneahedron," which is another word for a "nonahedron," a solid with nine faces. Another prefix for nine from the Greek language is "enneakis-."