vicennial

vicennial means occurring once every twenty years. Lexicurio rates it Sui generis — a strength score of 87 out of 100.

Etymology

From vicennium + -al or directly from Latin vīcenniālis, from vīcennium (“20-year span”) + -ālis (“-al”, adjective-forming suffix), from vīcennis (“20-year”) + -ium (“-ium”, suffix forming abstract nouns), from vīciēs (“20 times”) + annus (“year”) + -is (suffix forming compound adjectives). Equivalent to vice- (“twenty”) + -ennial.

adj

Occurring once every twenty years.
Lasting for twenty years.

noun

A twenty-year period“The maps are presented at 20-year intervals (vicennials) because of the nature of the data, particularly for years prior to 1960 when estimation procedures were not nearly as developed as today.”
A twentieth anniversary, particularly“Among the well established anniversaries celebrated by Chautauqua classes from year to year are the vicennials. A strong sense of comradeship is developed among members who come to Chautauqua twenty years after graduation...”
A twentieth anniversary, particularly; Synonym of vicennalia, the festival and religious ritual held in the 20th year of a Roman emperor's reign.“The feast of Constantine's vicennials fell on the 25th of July this year: it was the commencement of the twentieth year of his reign. It is supposed, that to avoid interrupting affairs or greater moment, this ceremony was deferred till the end of the council, which broke up the 25th of August.”