JAC'OBIN, noun [So named from the place of meeting, which was the monastery of the monks called Jacobines.] 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.
Source: Webster's 1828 American Dictionary ↗ · public-domain · returned verbatim, no AI