What is the X in X-mas?
early 14c., of the order of Dominican friars whose order built its first convent near the church of Saint-Jacques in Paris, from Old French Jacobin (13c.) "Dominican friar," also, in the Middle East, "a Copt;" see Jacob. The Revolutionary extremists took up quarters there October 1789. Used generically of radicals and allegedly radical reformers since 1793. Related: Jacobinism.