Bottomless Pit or the Abyss

Revelation 9:1 KJV 1900

And the fifth angel sounded, and I saw a star fall from heaven unto the earth: and to him was given the key of the bottomless pit.

Luke 8:31 KJV 1900

And they besought him that he would not command them to go out into the deep.

Romans 10:7 KJV 1900

Or, Who shall descend into the deep? (that is, to bring up Christ again from the dead.)

Revelation 11:7 KJV 1900

And when they shall have finished their testimony, the beast that ascendeth out of the bottomless pit shall make war against them, and shall overcome them, and kill them.

Revelation 17:8 KJV 1900

The beast that thou sawest was, and is not; and shall ascend out of the bottomless pit, and go into perdition: and they that dwell on the earth shall wonder, whose names were not written in the book of life from the foundation of the world, when they behold the beast that was, and is not, and yet is.

Revelation 20:3 KJV 1900

And cast him into the bottomless pit, and shut him up, and set a seal upon him, that he should deceive the nations no more, till the thousand years should be fulfilled: and after that he must be loosed a little season.

The Bottomless pit or the abyss.

12. ἄβυσσος ábussos; gen . abússou, fem. noun from a (1), an intens., and buthós (1037), deep. Abyss, an extremely deep place. It occurs only twice outside the book of Revelation (Rom. 10:7, simply the abode of the dead; Luke 8:31, the prison destined for evil spirits). In Rev. 9:1, 2; 11:7; 17:8; 20:1, 3, it is a prison in which evil powers are confined and out of which they can at times be let loose. It is not the lake of fire (Rev. 20:2, 10); nor is Satan regarded as being cast into this prison forever, but only to be so cast for one thousand years (Rev. 20:1, 2).