• WordNet 3.6
    • adj triennial occurring every third year or lasting 3 years
    • n triennial the 300th anniversary (or the celebration of it)
    • ***
Webster's Revised Unabridged Dictionary
    • Triennial Continuing three years; as, triennial parliaments; a triennial reign.
    • Triennial Happening, coming about, or appearing once in every three years; as, triennial elections; a triennial catalogue; a triennial visitation.
    • n Triennial Something which takes place or appears once in three years.
    • ***
Century Dictionary and Cyclopedia
    • triennial Continuing three years: as, triennial parliaments; specifically, of plants, lasting or enduring for three years.
    • triennial Happening every three years.
    • n triennial A mass performed daily for three years for the soul of a dead person.
    • n triennial A plant which continues to live for three years.
    • n triennial Any event, service, ceremony, etc., occurring once in three years; specifically, the third anniversary of an event.
    • ***
Chambers's Twentieth Century Dictionary
    • adj Triennial trī-en′yal continuing three years: happening every third year
    • ***


Webster's Revised Unabridged Dictionary
L. triennium, the space of three years; tri-,see Tri-) + annus, year. See Annual
Chambers's Twentieth Century Dictionary
L. triennistres, three, annus, a year.


In literature:

The number of graduates, as appears from the triennial catalogue, is 3,191.
"The New England Magazine, Volume 1, No. 1, January 1886" by Various
Oberlin has graduated, as shown by her last Triennial Catalogue, published in 1873, 579 men and 620 women.
"The Education of American Girls" by Anna Callender Brackett
We meet to-day under auspices how different from those which attended our last triennial assembling!
"The Atlantic Monthly, Volume 18, No. 107, September, 1866" by Various
The Third Triennial Report of the Commissioners of Woods was issued on the 18th of June, 1819.
"The Forest of Dean An Historical and Descriptive Account" by H. G. Nicholls
The species is easily recognized by the deciduous sheath and triennial cone.
"The Genus Pinus" by George Russell Shaw
The justices of the peace are chosen triennially, by the people.
"A New Guide for Emigrants to the West" by J. M. Peck
The rites triennial of the jovial god To tend.
"The Metamorphoses of Publius Ovidus Naso in English blank verse Vols. I & II" by Ovid
Mendelssohn's "Reformation" Symphony, and Schubert's Symphony in B minor, given at the Triennial Festival, Boston.
"Annals of Music in America" by Henry Charles Lahee
THE DIGNITY OF THE CHRISTIAN PRIESTHOOD, delivered to his Clergy at his Fourth Triennial Visitation.
"Notes and Queries, Number 239, May 27, 1854" by Various
A musical festival is held triennially.
"Encyclopaedia Britannica, 11th Edition, Volume 5, Slice 3" by Various

In news:

IARU President Tim Ellam, VE6SH, and IARU Secretary Rod Stafford, W6ROD -- attended the IARU Region 3 15th Triennial Conference on November 5-9 in Ho Chi Minh City, Vietnam.
IARU President Tim Ellam, VE6SH, and IARU Secretary Rod Stafford, W6ROD -- attended the IARU Region 3 15th Triennial Conference on November 5-9 in Ho Chi Minh City , Vietnam.
" Now that generation of emerging artists (born between the mid-1970s and the mid-'80s) is being called "The Ungovernables," at least by curators at the New Museum, organizing its second Triennial.
The Society of the Plastics Industry , Inc promoted Walt Bishop to the position of vice president in charge of trade shows SPI is the sponsor of the triennial NPE and Plastics USA events.
Koelnmesse's triennial Anuga FoodTec show in Cologne, Germany, spotlights Europe's latest equipment innovations.
After visiting "Intense Proximity," the Okwui Enwezor-curated Paris triennial at the Palais de Tokyo in June, I headed to Kassel, Germany, for another gigantic exhibition, Carolyn Christov-Bakargiev's dOCUMENTA 13.
Metro Receives "Clean" Triennial Review from Federal Transit Administration.
MMoCA's Wisconsin Triennial is all over the place, to its credit The anti-theme show Jennifer A.
2012 New Museum Triennial Danh Vo's "We the People," copper fragments of a full-size replica of the Statue of Liberty, is featured in this triennial .
Richard Masland, PhD, Professor of Ophthalmology and Patricia Donahoe, MD, Chief of Pediatric Surgical Services, Emeritus attended the Massachusetts General Hospital' Warren Triennial Prize Dinner that was held at the Liberty Hotel.
The New Museum in New York has just announced the list of artists included in its second Generational Triennial of emerging artists, scheduled to run Feb 15-Apr 22.
Officials from 16 IARU Member Societies in Region 3 attended the IARU Region 3 15th Triennial Conference.
At its triennial meeting in Montreal in early October, the ICAO Assembly–which includes representatives from all 187 ICAO member nations–approved a more flexible approach to the application of aircraft noise regulations.
Given the by now well-publicized lapses of its most notorious client, it came as something of a surprise this month when Enron's auditor, Arthur Andersen, passed its triennial peer review "without qualification".

In science:

This conference series, held under the auspices of the International Society on General Relativity and Gravitation provides a forum for a triennial review of all areas of research in gravitation, as well as an opportunity to look forward to and plan for future challenges.
Matters of Gravity, the newsletter of the Topical Group in Gravitation of the American Physical Society
Since no similar summary appeared in the last few triennial reports of the Commission, we review here the patterns seen in the last 14 issues, since the most recent change of editorship in 2001, but with emphasis on the most recent six issues.
Report IAU Comm. 42, Close Binary Stars
The power of such National Academy strategic planning is paralleled by that organized triennially by the NASA Office of Space Science.
Does the Lunar Surface Still Offer Value As a Site for Astronomical Observatories?