• synonyms


[trahy-en-ee-uh l]
  1. occurring every three years.
  2. lasting three years.
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  1. a third anniversary.
  2. something that appears or occurs every three years.
  3. a period of three years; triennium.
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Origin of triennial

First recorded in 1555–65; trienni(um) + -al1
Related formstri·en·ni·al·ly, adverb
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Examples from the Web for triennially

Historical Examples

  • The visits were repeated biennially till 1890, and then triennially.

    Encyclopaedia Britannica, 11th Edition, Volume 7, Slice 6


  • 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

British Dictionary definitions for triennially


  1. relating to, lasting for, or occurring every three years
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  1. a third anniversary
  2. a triennial period, thing, or occurrence
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Derived Formstriennially, adverb

Word Origin

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

Word Origin and History for triennially



1630s, "lasting three years;" 1640s, "occurring every three years," from Latin triennium "three-year period," from tri- "three" (see tri-) + annus "year" (see annual). For vowel change, see biennial.

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Online Etymology Dictionary, © 2010 Douglas Harper