triennium

noun
tri·​en·​ni·​um | \ trī-ˈe-nē-əm How to pronounce triennium (audio) \
plural trienniums or triennia\ trī-​ˈe-​nē-​ə How to pronounce triennia (audio) \

Definition of triennium

: a period of three years

First Known Use of triennium

1847, in the meaning defined above

History and Etymology for triennium

Latin, from tri- + annus year — more at annual

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