octaeteris

Borrowed from Ancient Greek ὀκταετηρίς (oktaetērís, “8-year [period]”).

octaeteris (plural octaeterides)

1. An octennium, a period of eight (8) years (chiefly) in the Ancient Greek calendar or in reference to the short lunisolar cycle.
   • 1852, Edward Greswell, “On the Lunar in Contradistinction to the Solar Modifications of the Primitive Calendar”, in Fasti Temporis Catholici and Origines Kalendariæ. [...] In Four Volumes, volume I, Oxford: At the University Press, OCLC 457298519, section V (The Octaëteris), pages 564:

     The octaëteris, or lunæsolar cycle of eight years, is a form of the lunar reckoning of annual time totally distinct from and independent of the reckoning of solar in the primitive equable calendar.

• octennium (rare)

• (adj.): octaeteric, octennial
• (19-year lunar cycle): Metonic cycle, enneadecaeteris
• (eight things): octad