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triennial

[trahy-en-ee-uh l] /traɪˈɛn i əl/
adjective
1.
occurring every three years.
2.
lasting three years.
noun
3.
a third anniversary.
4.
something that appears or occurs every three years.
5.
a period of three years; triennium.
Origin
1555-1565
1555-65; trienni(um) + -al1
Related forms
triennially, adverb
Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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British Dictionary definitions for triennially

triennial

/traɪˈɛnɪəl/
adjective
1.
relating to, lasting for, or occurring every three years
noun
2.
a third anniversary
3.
a triennial period, thing, or occurrence
Derived Forms
triennially, 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
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Word Origin and History for triennially

triennial

adj.

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.

Online Etymology Dictionary, © 2010 Douglas Harper
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