What is a 50 year period called? the celebration of any of certain anniversaries, as the twenty-fifth (silver jubilee ), fiftieth (golden jubilee ), or sixtieth or seventy-fifth (diamond jubilee ).
What is a half-century? a period of 50 yearsduring the past half-century.
Is 25 years a half-century? If semicentennial (semi-, precisely half, + centennial, a period of 100 years) is 50 years, then quarticentennial (quart-, a combining form meaning “a fourth,” + centennial) is properly the -ennial word meaning 25 years (and arguably more correct than quadrancentennial, since there is no combining form of quadrant).
What is 5 decades called? quinquennially kwin-ˈkwe-nē-ə-lē , kwiŋ- adverb.