tercentenary (adj.)youdaoicibaDictYouDict[tercentenary 词源字典]
1832, "pertaining to a period of 300 years," from ter- "three times" + centenary. As a noun from 1835. Related: Tercentennial (1862 as an adjective; 1872 as a noun).[tercentenary etymology, tercentenary origin, 英语词源]