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Epikoros (or Apikoros or Apikores or Epicurus; Hebrew: אפיקורוס, lit. "Heretic", pl. Epicorsim ) is a Jewish term cited in the Mishnah, referring to one who does not have a share in the world to come due to his casting off of the yoke of God and his commandments:
"All Israel have a share in the world to come as states: Your people are all righteous, they shall inherit the land for ever, the branch of My planting, the work of My hands, wherein I glory. And these are the ones who do not have a portion in the world to come: He who maintains that there is no resurrection of the dead derived from the Torah, and [He who maintains] that the Torah is not from the Heavens, and an Epikoros"
The rabbinic literature uses the term Epikoros, without a specific reference to the Greek philosopher Epicurus, yet it is apparent that the term is derived from the Greek philosopher's name, a philosopher whose views contradicted Jewish scripture, the strictly monotheistic conception of God in Judaism and the Jewish belief in the world to come.
"AN EPIKOROS. Rab and R. Hanina both taught that this means one who disrespects a Talmid Chacham [erudite Torah scholar]. R. Johanan and R. Joshua b. Levi maintained that it is one who disrespects his neighbour in the presence of a Talmid Chacham. "
Another root for the word is from the portmanteau of the two words api and keres, translated as face and cut off. This signifies that by the heretic having turned his face from God, he is punished by being cut off and excommunicated from both God and his Jewish brethren.
Maimonides combined the two commentaries, and according to him, scorning a Talmid Chacham is actually a singular case of disrespecting the entire Torah or its rabbinic scholar-sages. In his work Mishneh Torah (Yad, Teshuvah 3:8), Maimonides rules that an Epikoros is a person who denies that God communicates with humans through prophecy, or one who denies the prophecy of Moses, or one who denies God's knowledge of the affairs of humans  (i.e., one who maintains there is no divine providence). Maimonides probably encountered the name of Epicurus, the Greek philosopher, some time after composing his Commentary on the Mishnah and before composing The Guide for the Perplexed. In the first source he erroneously states that the rabbinic term epikoros is an Aramaic word, but in the Guide he has already become of aware of the atheistic doctrine of the philosopher by that name. He cites the source of his information as Alexander of Aphrodisias' treatise On Providence. 
Following the Christian censorship of the Talmud, starting with the aftermath of the Disputation of Barcelona and during the Roman Inquisition and the Spanish Inquisition, the term spread within the Jewish classical texts. Censors shunned expressions like minim ("sectary"), which they viewed referring to the Christian faith, and replaced them with the term Epikoros or Epicurus, hence an heretic, since the church would also fight the heretics. The censors also replaced terms that refer to Christians with the word akum, which stands for avodas kochavim. This term literally means "star worshippers", a belief that both Jews and their Christian censors abhorred.
- "Jewish Encyclopedia". Funk and Wagnalls. Retrieved 2013-03-30.
- "heresy" – Definition from Answers.com, including the content of Encyclopedia of Judaism
- "Teshuvah - Chapter Three". www.chabad.org.
- "Gadi Charles Weber, "Maimonides and the Epicurean Position on Providence," Review of Metaphysics 68:3 (March 2015): 545-572". The Review of Metaphysics. Retrieved 2015-04-17.