octaeteris

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

• (General American) IPA^(key): /ˌɑktaɪˈtɪɹɪs/
• (Received Pronunciation) IPA^(key): /ˌɒktaɪˈtɪəɹɪs/

octaeteris (plural octaeterides)

1. Synonym of octennium: An 8-year period, particularly (historical) in Greek calendrical and astronomical calculations.
   • 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 Oxford University Press, →OCLC, section V (The Octaëteris), page 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.

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