anniversary
/ˌænɪˈvɜːsərɪ/noun
(pl. -ies)
1- the date on which an event took place in a previous year周年纪念日：
the 50th anniversary of the Battle of Britain.
不列颠之战50周年纪念日。
1.1
- the date on which a country or other institution was founded in a previous year建国周年纪念日;成立周年纪念日：
the 75th anniversary of the RAF.
皇家空军成立75周年庆。
1.2
- the date on which a couple were married in a previous year结婚纪念日：
he even forgot our tenth anniversary!
他甚至忘了我们结婚十周年纪念日！
词源
Middle English: from Latin anniversarius 'returning yearly'， from annus 'year' + versus 'turning'.