"pertaining to a century and a half," 1875, from sesqui- + centennial (adj.). First in a notice of a "Sesqui-Centennial gathering" of descendants of Isaac and Ann Jackson, who settled in London Grove, Chester County, Pa., in 1725. As a noun, from 1880, first in reference to Baltimore's, probably short for sesquicentennial celebration, etc.
Resolution to close the City Hall offices during the Sesqui-Centennial after 12 M on the 12th 13th 11th 15th and 16th of October [Journal of Proceedings of the First Branch City Council of Baltimore, Tuesday, Oct. 5, 1880]
The alternative noun sesquicentenary or sesqui-centenary is attested from 1896 (in reference to Princeton's).
updated on June 06, 2022