triennial triene • trienniality · · · Info · Definitions · Synonyms · Characters · · triennial · · Text Latin · · Script 9 · · Length Definitions · · · (noun) the 300th anniversary (or the celebration of it). Synonyms: tercentennial, tercentenary. · · Noun Definition 1 (adj) occurring every third year or lasting 3 years. · · Adjective Definition 1 Synonyms · · · tercentennial · · Synonym 1 tercentenary · · Synonym 2 Characters · · a latin small letter a U+0061 e latin small letter e U+0065 i latin small letter i U+0069 l latin small letter l U+006C n latin small letter n U+006E r latin small letter r U+0072 t latin small letter t U+0074