Emily Dickinson Lexicon

JAC'O-BIN, n. [So named from the place of meeting, which was the monastery of the monks called Jacobins.]

The Jacobins, in France, during the late revolution, were a society of violent revolutionists, who held secret meetings in which measures were concerted to direct the proceedings of the National Assembly. Hence a Jacobin is the member of a club, or other person, who opposes government in a secret and unlawful manner or by violent means; a turbulent demagogue.