Synonyms: triennial, tercentenary, tercentennial
Definition: the 300th anniversary (or the celebration of it)
Similar words: day of remembrance, anniversary
Definition: the date on which an event occurred in some previous year (or the celebration of it)
Synonyms: triennial
Definition: occurring every third year or lasting 3 years
Similar words: periodic, periodical
Definition: happening or recurring at regular intervals
Usage: the periodic appearance of the seventeen-year locust