This chapter examines the images, feelings, connotations, and concepts that the word “terreur” evoked during the European Enlightenment. It first looks at a few definitions of terror before discussing the views of Paul-Henri Dietrich, Baron d'Holbach, a wealthy German nobleman who epitomized the Enlightenment war on terror. In particular, it considers Holbach's claim that philosophy is the cure for the psychological suffering caused by fear. It then explores the conception of terror as an attribute of God, which in turn associated it with majesty and justice, along with the practice of characterizing monarchs and nations as terrors. It also analyzes terror's connection to military science and law and punishment, including death penalty. Finally, it assesses the aesthetics of terror. The chapter shows that while the Enlightenment frequently railed against terror, its relationship to terror was highly ambivalent.