Noah Webster's New International Dictionary of the English Language

1. (a.) Returning with the year, at a stated time; annual; yearly; as, an anniversary feast.

2. (n.) The annual return of the day on which any notable event took place, or is wont to be celebrated; as, the anniversary of the Declaration of Independence.

3. (n.) The day on which Mass is said yearly for the soul of a deceased person; the commemoration of some sacred event, as the dedication of a church or the consecration of a pope.

4. (n.) The celebration which takes place on an anniversary day.