I did another search for the expression "second death" used in the Book of Revelation (see further below for the Biblical references) as spelled here (I just left out the article "hey":
11 מי אשר-אזן לו ישמע את אשר הרוח אמר לקהלות המנצח לא ינזק במות השני:
And found out that the two second lowest skips showed up in the same expression with a very obvious connection to this key term in the two verses below
Jer 51:57: "And I will make drunk her princes and her wise men, her governors and her deputies, and her mighty men; and they shall sleep a perpetual sleep, and not wake, saith the King, whose name is the LORD of hosts."
Jer 51:57 והשׁכרתי שׂריה וחכמיה פחותיה וסגניה וגבוריה ישׁנו שׁנת־עולםולא יקיצו נאם־המלך יהוה צבאות שׁמו׃ו
Jer 51:39: "With their poison I will prepare their feast, and I will make them drunken, that they may be convulsed, and sleep a perpetual sleep, and not wake, saith the LORD."
Jer 51:39 בחמם אשׁית את־משׁתיהם והשׁכרתים למען יעלזו וישׁנו שׁנת־עולם ולא יקיצו נאם יהוה׃
"Sleep" is often used in the Bible as a synonym of death:
John 11:11: "These things said He: and after that He saith unto them, 'Our friend Lazarus sleepeth; but I go, that I may awake him out of sleep'. 12 Then said His disciples, 'Lord, if he sleep, he shall do well.' 13 Howbeit Jesus spake of his death: but they thought that He had spoken of taking of rest in sleep. 14 Then said Jesus unto them plainly, 'Lazarus is dead'."
See also:
Daniel 12:2: "And many of them that sleep in the dust of the earth shall awake, some to everlasting life, and some to shame and everlasting contempt."
Here are the verses where the expression "second death" is used in the NT:
Rev 2:11: "He who has an ear, let him hear what the Spirit says to the churches. He who overcomes will not be hurt by the second death."
Rev 20:6: "Blessed and holy is he who has part in the first resurrection. The second death has no authority over these, but they will be priests of God and of Christ, and will reign with Him a thousand years."
Rev 20:14: "And death and hell were cast into the Lake of Fire. This is the second death."
Rev 21:8: "But the fearful, and the unbelieving, and the abominable, and murderers, and whoremongers, and sorcerers, and idolaters, and all liars, will have their part in the Lake burning with fire and brimstone, which is the second death."
The second death is equivalent to the "Lake of Fire" (cf Rev 20:14, 21:8), were are told elsewhere that it is perpetual:
Rev 20:10: "And the Devil who deceived them was cast into the Lake of Fire and Brimstone, where the beast and the false prophet were. And he will be tormented day and night forever and ever."