Definition of "Tartarus"

[…] them with Fire and hoſtile Arms / Fearleſs aſſault, and to the brow of Heav'n / Purſuing, drive them out from God and bliſs, / Into thir place of puniſhment, the Gulf / Of Tartarus, which ready opens wide / His fiery Chaos to receave thir fall.

1667, John Milton, “Book VI”, in Paradise Lost. […], London: […] [Samuel Simmons], […]; republished as Paradise Lost in Ten Books: […], London: Basil Montagu Pickering […], 1873, lines 50–55

We lay there hour after hour in terror and misery of mind so deep that I will not attempt to describe it, and listened to the wild storm-voices of that Tartarus, as, set to the deep undertone of the spur opposite against which the wind hummed like some awful harp, they called to each other from precipice to precipice.

1886 October – 1887 January, H[enry] Rider Haggard, She: A History of Adventure, London: Longmans, Green, and Co., published 1887

After arranging a rendezvous, we separate. Mattie and Liz go off in one direction, and Em and I in another. From this our progress seems like a descent into Tartarus. Em pauses before a miserable-looking saloon, pushes open the low, swinging door, and we go in.

1890, William Booth, “Round the slums of New York”, in In Darkest England and the Way Out‎, page 161