triennial

Triennial is a term used to describe something that occurs every three years or lasts for a three-year period. As an adjective, it qualifiers cycles, events, reports, or programs tied to a three-year interval. As a noun, a triennial refers to an event scheduled on a three-year cycle, such as certain international exhibitions, conferences, or competitions. In botany, a triennial plant completes its life cycle in three years, typically growing during the first two years and flowering or setting seed in the third.

The word comes from Latin tri- meaning three and annus meaning year, and it entered English in the early modern period. The concept is commonly contrasted with biennial (every two years) and with terms describing events that occur three times in a year, such as triannual, though triannual can lead to ambiguity.

Common contexts for triennial usage include arts, design, science, and organizational planning, where a three-year cycle governs elections, grants, or major exhibitions. In scheduling, a triennial approach can align with long-term strategic goals, provide stable planning horizons, and allow for multi-year project development.

Notes on terminology: triennial should not be confused with triannual, which more often implies three times within a single year. The term tricennial or tricennially is rare and may be encountered in historical or ceremonial contexts, but triennial remains the standard designation for three-year cycles.