The word "arch fiend" refers to a powerful and malevolent demon or evil spirit. Some antonyms for this term might include "angel," "savior," "hero," or "protector." These words describe beings or figures that are associated with goodness, light, and benevolence. While arch fiends are often seen as antagonistic figures in mythology and popular culture, angels and other positive figures are celebrated for their purity and guardianship over humanity. The use of these antonyms can serve to contrast the negative associations of the term "arch fiend" with more positive, hopeful concepts.