An "arch-villain" is typically a primary antagonist in literature or media, but there are plenty of synonyms that can also be used to describe a villainous character. The term "antagonist" is a more general synonym that can apply to any character who opposes the protagonist. Other synonyms for "arch-villain" include "nemesis," "adversary," "foe," and "opponent." These terms can be used in a broader sense to describe any character who challenges the protagonist, but they still imply a sense of antagonism and opposition. Regardless of the synonym chosen, a well-written villain can be just as memorable and impactful as the hero.