triennial

tri·en·ni·al  (tr-n-l)

adj.

1. Occurring every third year.

2. Lasting three years.

n.

1. A third anniversary.

2. A ceremony or celebration occurring every three years.

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[From Latin triennis, from triennium, triennium; see triennium.]

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tri·enni·al·ly adv.

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triennial [traɪˈɛnɪəl]

adj

n relating to, lasting for, or occurring every three years

1. a third anniversary

2. a triennial period, thing, or occurrence

[from Latin triennium]

triennially  adv

Thesaurus

Noun	1.	triennial - the 300th anniversary (or the celebration of it) tercentenary, tercentennial anniversary, day of remembrance - the date on which an event occurred in some previous year (or the celebration of it)
Adj.	1.	triennial - occurring every third year or lasting 3 years periodic, periodical - happening or recurring at regular intervals; "the periodic appearance of the seventeen-year locust"

Translations

triennial [traɪˈenɪəl] ADJ → trienal

triennial

adj (= lasting 3 years) → dreijährig; (= every 3 years) → dreijährlich, alle drei Jahre stattfindend