octaeteris
/ˌɒktʌɪˈtɪərɪs/noun
In the ancient Greek calendar: a period of eight years, in the course of which three months of 30 days each were intercalated so as to make the year of 12 lunar months correspond with the solar year.
Origin
Mid 17th century. From post-classical Latin octaeteris (3rd cent.) or its etymon ancient Greek ὀκταετηρίδ-, ὀκταετηρίς period of eight years from ὀκτα- + ἔτος year.