🔼The name Leb-kamai in the Bible
It's not clear whether Leb-kamai (or even just Leb) is a Biblical name, or rather in which sense the prophet Jeremiah (or a later editor) meant to use it. It occurs only once in the Bible, namely in Jeremiah 51:1, where YHWH declares that He will arouse a destroying spirit against Babylon and against "the settlers of Leb-kamai". Of the major modern English translations, only the ASV, NAS, NIV and JSP speak of Leb-kamai. The KJV has "them that dwell in the midst of them that rise up against me," and the Darby Translation has the similar "them that dwell in the heart of those that rise against me". The Young Translation, uniquely, has "the inhabitants of Leb -- My withstanders".
Leb-kamai may be a region or city but no other writer mentions it, which suggests that it wasn't very significant. And that makes it rather odd that it is mentioned as singled-out victim of a destroying force that is potent enough to sack Babylon. Some scholars (as endorsed by BDB Theological Dictionary) suggest that Leb-kamai (לב קמי) was another name for the Gambulai (קמבלי), which was an unmentioned nomadic tribe in the south of Chaldea, but this theory lacks any compelling evidence and also doesn't explain why Jeremiah would use this alternate name.
Other scholars have pointed out that when we run our name through the Athbash cypher (replacing the letter א with the ת, the letter ב with the ש, and so on), we get כש דים, Kesedim, which is Hebrew for Chaldeans. The name Sheshach appears to be another instance of this (Jeremiah 25:26, 51:41), but it's not clear why Jeremiah thought it necessary to create or utilize these nicknames. It may very well be that Jeremiah used a kind of code which neither Babylonian security nor modern Scripture theorists have been able to crack.
In other words, there are reasons galore to construe Leb-kamai as the name of a specific region in Babylon, but very little material to explain why Jeremiah would zoom in on this particular region. Perhaps there is yet undiscovered portent in this particular instance of employ of the Athbash cypher, and perhaps the phenomenon is a cute coincidence and nothing more. All things considered, the phrase Leb-kamai appears to makes most sense when it's considered as part of the narrative, and describing a condemning quality of Babylon itself:
🔼Etymology of the name Leb-kamai
The pseudo-name Leb-kamai consists of two elements. The first part of our name is the word לב (leb), meaning heart:
The second part of our name could convincingly be drawn from the root-verb קום (qum), meaning to rise up or stand:
The final letter י (yod) is the mark of a possessive form or an adjective.
The phrase Leb-kamai means Heart Of Uprising or rather Elevated Heart, but it seems to not be derogative, as is suggested by the KJV, Darby and Young interpretations. Leb-kamai rather confirms the glory and superiority of Babylon, but accuses it of its prideful neglect to give the Creator His due honors.
The core sentiment of this pseudo-name is possibly also expressed in Revelation 17:1-6 and particularly in Revelation 18:7, where is said of Babylon the Great: "for she says in her heart, 'I sit as a queen and I am not a widow, and will never see mourning".