late O.E., from L. September, from septem "seven" (see seven). So called because it was the seventh month of the old Roman calendar, which began the year in March; Julian calendar reform (46 B.C.E.) shifted the new year back two months. For -ber suffix, see
December. Replaced O.E. hærfestmonað, haligmonað. Septembrist (1840) in Fr. history refers to the massacre of the political prisoners in Paris, Sept. 2-5, 1792.