A two-hundredth anniversary; a 200-year period or the celebration of such a milestone.
From bi- (two) + centennial (from Latin centum meaning hundred + annum meaning year). Became prominent in American English in the 1970s.
America's 1976 Bicentennial was the biggest party the nation had thrown in decades—the entire country decorated itself red, white, and blue to celebrate 200 years!
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