In 2 Pet 2:4, we read the following:
For if God did not spare the angels when they sinned, but cast them into hell and committed them to chains of deepest darkness to be kept until judgment. (NRSV)
"Cast [them] into hell" comes from the verb ταρταρόω, which means "to cast into Tartarus." This verb is used only in this verse in the Greek New Testament; notwithstanding, it appears in other Greek texts pre-dating the New Testament. BDAG defines the verb thusly:
7265 ταρταρόω
• ταρταρόω (Τάρταρος ‘the Netherworld’) 1 aor. ἐταρτάρωσα (Acusilaus Hist. [V BC]: 2 fgm. 8 Jac. I p. 50; Lydus, Men. 4, 158 p. 174, 26 W.; cp. Sext. Emp., Pyrrh. Hypot. 3, 24, 210 ὁ Ζεὺς τὸν Κρόνον κατεταρτάρωσεν [this compound several times in Ps.—Apollod.: 1, 1, 4; 1, 2, 1, 2; 1, 2, 3]. Tartarus, thought of by the Greeks as a subterranean place lower than Hades where divine punishment was meted out, and so regarded in Israelite apocalyptic as well: Job 41:24; En 20:2; Philo, Exs. 152; Jos., C. Ap. 2, 240; SibOr 2, 302; 4, 186) hold captive in Tartarus 2 Pt 2:4.—DELG s.v. Τάρταρος. M-M.
With respect to the Enochian literature, 1 Enoch 20:2 reads:
Οὐριήλ, ὁ εἷς τῶν ἁγίων ἀγγέλων ὁ ἐπὶ τοῦ κόσμου καὶ τοῦ ταρτάρου.
Uriel, one of the holy angels, the one over the world and Tartarus.
It is clear that Peter is appealing to the myth of fallen angels from Enochian traditions in his comments, as did Jude in the parallel passage in Jude 6:
And the angels who did not keep their own position, but left their proper dwelling, he has kept in eternal chains in deepest darkness for the judgment of the great Day. (NRSV)
It is rather clear that both Peter and Jude are affirming the existence of fallen angels and, furthermore, that they are appealing to Enochian traditions positively to make their arguments against their opponents. Furthermore, it highlights the importance of knowing extra-canonical texts to help engage in exegesis of the biblical texts.
Further reading:
Archie T. Wright, The Origin of Evil Spirits: The Reception of Genesis 6:1-4 in Early Jewish Literature
