archfiend means A chief fiend (devil, demon or monster). Lexicurio rates it Sui generis — a strength score of 87 out of 100.
archfiend is pronounced /ˈɑɹt͡ʃ.find/.
Why “archfiend” is a great word
ARCHFIEND — [Noun] A chief or supreme fiend, especially Satan, or a person of diabolical evil. From the prefix arch- ("chief, principal") + fiend ("demon, devil"). First recorded in English 1660–70. Unlike a "fiend," a general term for a wicked entity, or a "demon," a malevolent spirit among many, an archfiend is the paramount source, the organizing principle of malice. It is the architect of ruin, the cold intelligence in the eye of the storm, the dark sun around which all lesser evils orbit—the chilling recognition that malice, too, has its lonely, absolute throne.
Etymology
From arch- + fiend. Compare German Erzfeind, Dutch aartsvijand.
noun
- A chief fiend (devil, demon or monster).“Of those [spirits] who rebelled some became devils, fiends or archfiends, according to the manifold proportions of their transgression.”
- Satan.“So stretcht out huge in length the Arch-fiend lay
Chain’d on the burning Lake,”
- A diabolically evil person.“1690, anonymous translator, The Royal Wanton (attributed to Gregorio Leti), London: F.B., Part 5, p. 48,
[…] her Arch-fiend and Devil of a Lord, had impudently sent the same Villain to abuse her once again.”