
1) Chief foe 2) Lex luthor, to superman 3) Most difficult foe 4) Nemesis 5) Satan 6) The Devil 7) The joker, to batman 8) Voldemort, to Harry Potter
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https://www.crosswordclues.com/clue/archenemy

1) Nemesis
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https://www.crosswordclues.com/clue/archenemy

An archenemy, archfoe, archvillain, or nemesis (sometimes spelled arch-enemy, arch-foe, or arch-villain originated around the mid-16th century) is the principal enemy of someone or something. In fiction, it is a character who is the hero/protagonist`s worst enemy. == Etymology == The word archenemy or arch-enemy originated around the mid-16th cen....
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http://en.wikipedia.org/wiki/Archenemy

• (n.) A principal enemy. Specifically, Satan, the grand adversary of mankind.
Found on
http://thinkexist.com/dictionary/meaning/archenemy/
Arch`en'e·my noun [ Prefix
arch- +
enemy .] A principal enemy. Specifically, Satan, the grand adversary of mankind.
Milton. Found on
http://www.encyclo.co.uk/webster/A/115

archenemy A chief enemy; someones main or worst enemy.
Found on
http://www.wordinfo.info/words/index/info/view_unit/104/

a chief enemy. · Satan; the Devil.
Found on
https://www.infoplease.com/dictionary/archenemy
No exact match found.