diamond jubilee
noun /ˌdaɪmənd ˈdʒuːbɪliː/
/ˌdaɪmənd ˈdʒuːbɪliː/
[usually singular]- the 60th anniversary of an important event, especially of somebody becoming king/queen; a celebration of this event
- Queen Victoria had been on the throne for 60 years and her diamond jubilee was being celebrated.