Jacobin
Technically, this was a political party during the French Revolution. But I don’t think it gets used in that sense much.
Today, it seems to just mean “political radical,” particulary from the Left. In fact, an American socialist magazine is named Jacobin.
The name comes from their first headquarters, a former monastery in Paris.
Why I Looked It Up
From It's Good to Be a Man:
As the Jacobins were putting the political and social order at the heart of Christendom into a blender, people like Mary Wollstonecraft were doing the same to the sexual order that God made on the sixth day of creation.