From Longman Dictionary of Contemporary Englishtercentenaryter‧cen‧te‧na‧ry /ˌtɜːsenˈtiːnəri $ ˌtɜːrsenˈtenəri, tɜːrˈsentəneri/ noun (plural tercentenaries) [countable] British English TMCthe day or year exactly 300 years after a particular event
Examples from the Corpus
tercentenary• The tercentenary of the first Bill, passed in 1688, has provided a stimulus for some earnest reflection.Origin tercentenary (1800-1900) Latin ter “three times” + English centenary 