vigentennial

[ vahy-jen-ten-ee-uh l ]
/ ˌvaɪ dʒɛnˈtɛn i əl /

noun

a 20th anniversary.
a celebration, meeting, reunion, etc., commemorating such an anniversary.

Origin of vigentennial

< Latin vīgēn(ī) twenty each + (cen)tennial
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019