Triennial1. (a.) Happening or appearing once in every three years; as, triennial elections; a triennial visitation.
2. (a.) Continuing three years; as, triennial parliaments; a triennial reign.
3. (n.) Something which takes place or appears once in three years.
Thesaurus Entries
amphibian, angiosperm, anniversary, annual, annual holiday, aquatic plant, biannual, bicentenary, bicentennial, biennial, bimonthly, birthday, bissextile day, biweekly, catamenial, centenary, centennial, commemoration, cosmopolite, cutting, daily, decennial, deciduous plant, diamond jubilee, dicot, dicotyledon, diurnal, ephemeral, evergreen, exotic, flowering plant, fortnightly, fungus, gametophyte, golden wedding anniversary, gymnosperm, hebdomadal, holy days, hourly, hydrophyte, immovable feast, jubilee, leap year, menstrual, momentary, momently, monocot, monocotyl, monthly, name day, natal day, octennial, perennial, plant, polycot, polycotyl, polycotyledon, quadrennial, quarterly, quasquicentennial, quincentenary, quincentennial, quinquennial, quotidian, secular, seed plant, seedling, semestral, semiannual, semimonthly, semiweekly, semiyearly, septennial, sesquicentennial, sextennial, silver wedding anniversary, spermatophyte, sporophyte, tercentenary, tercentennial, tertian, thallophyte, tricennial, vascular plant, vegetable, wedding anniversary, weed, weekly, yearly