The Collaborative International Dictionary
Enneatical
Enneatic \En`ne*at"ic\, Enneatical \En`ne*at"ic*al\, a. [Gr. 'enne`a nine.] Occurring once in every nine times, days, years, etc.; every ninth.
Enneatical day, every ninth day of a disease.
Enneatical year, every ninth year of a man's life.
Wiktionary
enneatical
a. Occurring once in every nine times, days, years, etc.; every ninth.