early 14c., "Dominican friar," from Old French Jacobin (13c.) "Dominican friar" (also, in the Middle East, "a Copt"); so called because the order built its first convent near the church of Saint-Jacques in Paris. The masc. proper name Jacques is from Late Latin Iacobus, for which see Jacob.
The Revolutionary extremists ("Society of the Friends of the Constitution") made their club headquarters there October 1789 and supported Robespierre during the Terror. They were suppressed along with him in November 1794 and many members executed. In English, the word quickly became a scare-word for the worst excesses of the French Revolution, and since 1793 it has been used generically and often inappropriately of allegedly radical politicians and reformers. Related: Jacobinism; Jacobinic; Jacobinical.