decennalia
The festival and religious rituals celebrating a Roman emperor's 10th year of rule.
historical
Seven pieces celebrate the Decennalia of Arcadius, which were due on Jan. 15, 393.
Where it comes from
From Latin decennālia, from decennium (“10-year period”) + -ālia (“-alia: forming the names of festivals”), from decennis (“10-year”) + -ium (“-ium: forming abstract nouns”). Equivalent to decennium + -alia.
Adapted from the Wiktionary entry decennalia (CC BY-SA 4.0).