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vicennial

[vahy-sen-ee-uh l]
adjective
  1. of or for 20 years.
  2. occurring every 20 years.

Origin of vicennial

1730–40; < Latin vīcenni(um) twenty-year period (vīc(ēnī) twenty each + -enn(us), combining form of annus year + -ium -ium) + -al1
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
British Dictionary definitions for vicennial

vicennial

adjective
  1. occurring every 20 years
  2. relating to or lasting for a period of 20 years

Word Origin for vicennial

C18: from Late Latin vīcennium period of twenty years, from Latin vīciēs twenty times + -ennium, from annus year
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012