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bicentennial

adjective

pertaining to or in honor of a 200th anniversary: bicentennial celebration; a bicentennial exposition.
consisting of or lasting 200 years: a bicentennial period.
occurring every 200 years: the bicentennial return of a comet.

noun

a 200th anniversary: The United States had its bicentennial in 1976.
a celebration of such an anniversary.

also bi-centennial, 1843 (adj.), 1871 (noun), American English, from bi- + centennial (q.v.). In rivalry with bicentenary (1831) which seems to have been the more common word in Britain.