quindecennial

== English == === Etymology === From Latin quindecennialis, from quindecennium (“15-year period”) + -alis (“-al: forming adjs”). Equivalent to quindec- +‎ -ennial. === Adjective === quindecennial (not comparable) Lasting fifteen years. Happening once in fifteen years. === Further reading === “quindecennial”, in OneLook Dictionary Search.