Source : Webster's Revised Unabridged Dictionary (1913)

Enneatic \En`ne*at"ic\, Enneatical \En`ne*at"ic*al\, a. [Gr. ?
   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.