APIKOROS, in popular usage, one who negates the rabbinic tradition. The designation apikoros first occurs in rabbinic literature in the Mishnah (Sanh. 10:1), enumerated among those who forfeit their "share in the world to come." Although there is no doubt that the name is derived from the Greek Επικουρος (see *Epicureanism), the rabbis seem to have been unaware of, or ignored, the Greek origin of the word and took it to be connected with the Aramaic word hefker ("abandoned"; see TJ, Sanh. 10:1, 28b; cf. also Maimonides' introduction to the above Mishnah, which explicitly states that it is an Aramaic word). They extended its meaning to refer generally to anyone who throws off the yoke of the commandments, or who derides the Torah and its representatives. Thus *Korah, who, according to the rabbis, held up the laws of the Torah to ridicule, is referred to as an apikoros (TJ, Sanh. 10:1, 27d). The most extensive discussion is to be found in Sanhedrin 99b–100a where different amoraim of the third and fourth centuries apply the term variously to one who insults a scholar, who insults his neighbor in the presence of a scholar, who acts impudently toward the Torah, who gibes and says "what use are the rabbis to us, they study for their own benefit," or "what use are the rabbis since they never permitted us the raven nor forbade us the dove" (i.e., who cannot go beyond the dictates of the Torah). Maimonides gives a more precise theological definition of the word. Distinguishing the apikoros from the sectarian (min), the disbeliever, and the apostate, he defines him as one who either denies prophecy, and therefore the possibility of communion between God and man, or denies divine revelation ("who denies the prophecy of Moses"), or who says that God has no knowledge of the deeds of man (Maim., Yad, Teshuvah 3:8). Later authorities extended the meaning even further to include all those who refuse obedience to the rabbis, even "the authority of a religious work, great or small" (Moses Ḥagiz, Leket ha-Kemaḥ YD 103a). In modern parlance, it is popularly used loosely for anyone who expresses a view which is regarded not only as heretical but even as heterodox.
Guttmann, Mafte'aḥ, 3 pt. 2 (1930), 9–14.