occurring every three years.
lasting three years.
a third anniversary.
something that appears or occurs every three years.
a period of three years; triennium.
Origin of triennial
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
Examples from the Web for triennially
Historical Examples of triennially
The visits were repeated biennially till 1890, and then triennially.
Some unions meet annually, some biennially, some triennially, and a few determine by referendum when the convention is to meet.The Armies of Labor
Samuel P. Orth
relating to, lasting for, or occurring every three years
a third anniversary
a triennial period, thing, or occurrence
Word Origin for triennial
C17: from Latin triennium
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
Online Etymology Dictionary, © 2010 Douglas Harper