Here's A. T. Robertson's entry in his Word Pictures in the New Testament.
Cast them down to hell (ταρταρωσας [tartarōsas]). First aorist active participle of ταρταροω [tartaroō], late word (from ταρταρος [tartaros], old word in Homer, Pindar, LXX Job 40:15; 41:23, Philo, inscriptions, the dark and doleful abode of the wicked dead like the Gehenna of the Jews), found here alone save in a scholion on Homer. Ταρταρος [Tartaros] occurs in Enoch 20:2 as the place of punishment of the fallen angels, while Gehenna is for apostate Jews.The plot thickens. Jude quotes from the book of Enoch, which speaks of Tartaros as the place of punishment of the fallen angels, exactly as stated in Peter. And both Jude and Peter spoke of the angels kept in chains:
Jude 1:6 And the angels which kept not their first estate, but left their own habitation, he hath reserved in everlasting chains under darkness unto the judgment of the great day.
2 Peter 2:4 For if God spared not the angels that sinned, but cast them down to hell [tartarus], and delivered them into chains of darkness, to be reserved unto judgment;Both Peter and Jude speak of fallen angels chained in darkness. This is the standard Greek mythology about Tartarus. Here's a snippet from the wiki article:
When Zeus ordered Thanatos to chain Sisyphus in Tartarus upon his death, Sisyphus tricked Thanatos by asking him how the chains worked and ended up chaining Thanatos which caused no one to die.Note that "Thanatos" is Death personified. This is the exact name of the Rider of the Fourth Horse in Revelation! This is pure, unadulterated Greek mythology. Indeed, we now enter into a full frontal display of pagan Greek mythology complete with the pantheon of imaginary gods in R. J. Bauckham's entry in the Word Biblical Commentary:
ἀλλὰ σειραῖς ζόθου ταρταρώσας ηαρέσωκεν, “but cast them into hell and committed them to fetters of nether darkness.” The verbs ταρταροῦν and (rather more common) καταταρταροῦν mean “to cast into Tartarus,” and were almost always used with reference to the early Greek theogonic myths, in which the ancient giants, the Cyclopes and Titans, were imprisoned in Tartarus, the lowest part of the underworld, by Uranos, Kronos and Zeus (Pearson, GRBS 10  76–78). They are not used in the Greek version of 1 Enoch,; though τάρταρος (“Tartarus”) is used of the place of divine punishment in 1 Enoch 20:2, as elsewhere in Jewish Greek literature (LXX Job 40:20; 41:24; Prov 30:16; Sib. Or. 4:186; Philo, Mos. 2.433; praem 152). But Hellenistic Jews were aware that the Greek myth of the Titans had some similarity to the fall of the Watchers (though Philo, Gig. 58, rejects any comparison). Sometimes the Watchers’ sons, the giants (the Nephilim), were compared with the Titans (Josephus, Ant. 1.73; cf. LXX Ezek 32:27; Sir 16:7) but in Jdt 16:6 (and also the Christian passage Sib. Or. 2:231) the Watchers themselves seem to be called τιτᾶνες (“Titans”). Thus in using a term reminiscent of the Greek myth of the Titans the author of 2 Peter follows Hellenistic Jewish practice.Say what? I'm reading a commentary on the Christian Bible, the source book for the truth about heaven and hell and I am being told that the fallen angels were tossed into Tartarus, the same place that the pagan gods Uranos, Chronos, and Zeus threw the Cyclopes and Titans?
Suddenly, this doesn't sound like a "Bible" study at all! Zeus? Chronos? Titans? This is "God's truth"???
We've got some work to do folks! How is it possible that we all have been studying Scripture all these years and haven't noticed these facts? Willful ignorance? I know I'll be reflecting on this for a while.