Enneadic is an adjective that means "relating to the number nine," or "occurring once every nine years." Although it is a somewhat rare word, there are several synonyms that can be used in its place. These include nonary, denary, novenary, and enneal. Nonary is probably the most commonly used of these, and can refer to anything related to the number nine. Denary refers specifically to the number ten, but can also be used to refer to groups of nine or ten. Novenary is often used in reference to astrology or other mystical practices, while enneal is a more technical term used in mathematics.