1. Happening once every 20 years.
2. Existing or lasting for 20 years.
1. occurring every 20 years
2. relating to or lasting for a period of 20 years
[C18: from Late Latin vīcennium period of twenty years, from Latin vīciēs twenty times + -ennium, from annus year]
vi•cen•ni•al(vaɪˈsɛn i əl)
1. of or for twenty years.
2. occurring every twenty years.
[1730–40; < Latin]
|Adj.||1.||vicennial - occurring once every 20 years|