Tricennial

Part of speech: adjective

Definitions

1. Happening or recurring at intervals of thirty years ; lasting or enduring for three hundred years
2. Taking place once every three decades ; extending across a span of three centuries
3. Returning or observed every thirty years ; pertaining to a period of three hundred years in duration

Etymology: "Tricennial" describes something that happens every thirty years or lasts thirty years, and its making is a neat piece of Latin arithmetic. The Romans had "trīciēs," meaning "thirty times," which combined with "annus," the word for year, to give "trīcennium," a period of thirty years. From that came the adjective "trīcennālis," and English took the idea through the Latin base, so the word is built on the same pattern as "decennial," a ten-year span, with "tri-" swapped in for "dec-." The English form is therefore a doublet of "tricennal," which came from the same Latin adjective by a slightly different route. Both words mean the same thing, and they sit side by side in the language as close relatives rather than one replacing the other.