semicentenary
semicentennial

Officially opened on 10 October 1975, it commemorates the semicentenary of Afrikaans being declared an official language of South Africa separate from Dutch.

His wife was the editor of the Semicentenary of the University of California, a volume issued by the University Press at Berkeley in 1920.

Additionally, Rockland Community College celebrated the institution's Semicentennial, quinquagenary or Golden Anniversary from September 2009 through August 2010.