vicennial

The story

1. Latin · borrowed fromvīcenniālis
2. English todayvicennial

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.