anniversary

noun3

1. •
   the date on which something important once happened, when it comes again in a later year

   • Today is the fiftieth anniversary of the end of the war.
   • A 'millennium' is a thousand-year anniversary.
2. •
   Such a day that commemorates a wedding.

   • We are celebrating our tenth anniversary today.
3. •
   A day subsequent in time to a given event by some significant period other than a year (especially as prefixed by the amount of time in question).

   • The occasion was the six-month anniversary of the Aug. 8 coup that brought General Óscar Humberto Mejía Victores to power. — 1984