anniversary
/ˌænɪˈvɜːs(ə)ɹi/noun
The date each year that marks an exact number of years since an important event took place.
Example sentences
- “They celebrate their wedding anniversary every June.”
- “The museum is celebrating its hundredth anniversary with free entry all week.”
Built on the Latin for "year", so a "six-month anniversary" is loose usage. Unmodified, it usually means a wedding anniversary.