septicentennial noun2 •700th anniversary.His septicentennial in 1984 occasioned widespread congresses and celebrations, not least in the United States, including an Alfonsine exhibit at the Library of Congress. — 2012 •The celebration of a 700th anniversary.As the sun neared the mountain range in the west, group after group of the septicentennial participants began leaving the head temple reluctantly but orderly, under the direction of the Soka Han. — 1991 formssepticentennials
