'Vicennial' definitions:

Definition of 'vicennial'

(from WordNet)
adjective
Occurring once every 20 years

Definition of 'Vicennial'

From: GCIDE
  • Vicennial \Vi*cen"ni*al\, a. [L. vicennium a period of twenty years; viceni twenty + annus year.]
  • 1. Lasting or comprising twenty years. [1913 Webster]
  • 2. Happening once in twenty years; as, a vicennial celebration. [1913 Webster]