Main Entry: tri·en·ni·al

Pronunciation: \(ˌ)trī-ˈe-nē-əl\

Function: adjective

Date: 1562

1 : occurring or being done every three years <the triennial convention>
2 : consisting of or lasting for three years <a triennial contract>

— triennial noun

— tri·en·ni·al·ly \-nē-ə-lē\ adverb