Which term refers to an act of extreme wickedness?

The term that refers to an act of extreme wickedness is "enormity." Historically, enormity has been used to describe actions that are not only significant in scale but are also morally reprehensible or evil. It conveys a sense of something that is not just large or extensive, but also profoundly immoral or unacceptable. This connotation is crucial when discussing extreme acts, as it highlights the gravity of the wickedness involved.

In contrast, the other terms do not carry the same implications of wickedness. An "epithet" is a descriptive phrase or term that characterizes someone or something, often used in a neutral or even positive sense. An "encomium" refers to a formal expression of praise, thus lacking any negative connotation. "Effluvia" pertains to noxious or harmful fumes or odors, which, while unpleasant, do not imply the moral weight associated with acts of wickedness.