Noun
The 75th anniversary of some event, particularly a wedding.
The 60th anniversary of some event, particularly a wedding.
Source: en.wiktionary.orgBrian and Gillian Wood will celebrate their diamond anniversary on Thursday, May 17, having got married on that date in 1958 at St Mary's Catholic Church, in Balance Street, Uttoxeter. Source: Internet
Or its diamond anniversary, depending on how traditional you are. Source: Internet