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Fausset's Bible Dictionary [1]

 Jeremiah 25:26;  Jeremiah 51:41; i.e. Babylon, from their goddess Shach reduplicated, as they named Misael Meshach. SHACE was the designation of a Babylonian feast to Shach, of five days' duration, during which unbridled license prevailed as at the Roman saturnalia. Slaves ruled their master, and one called zogan in each house in royal garments ruled the rest ( Jeremiah 51:39;  Jeremiah 51:57;  Isaiah 21:5). Cyrus during it took Babylon; thus Jeremiah prophesies the concomitants of the capture. The Kabalistic system ( Αthbash , "The First Hebrew Letter Being Expressed By The Last, The Second By The Last But One," Etc.) would make Sheshach answer to Βabel . But in  Jeremiah 51:41 concealment cannot have been Jeremiah's object, for he mentions "Babylon" ( Jeremiah 51:42). It is not likely the Kabala was as yet invented.

Morrish Bible Dictionary [2]

Mystical name applied to Babylon.  Jeremiah 25:26;  Jeremiah 51:41; cf.  Jeremiah 51:1 . The meaning of the word is not known. According to Jerome the name Babylon, from Babel, was made up of the letters B B L (the 2nd and the 12th letters of the Hebrew alphabet) these were changed into SH SH CH (the 2nd and the 12th letters reckoning from the end of the same alphabet), a mode well known to later Jews. It has been supposed that the Jews made this alteration in the name in order that they might speak of the judgements coming upon Babylon without giving offence to those who had carried them away captive.

Hastings' Dictionary of the Bible [3]

Sheshach . A cryptic name of Babel, found in the received text of   Jeremiah 25:26;   Jeremiah 51:41 . It is formed by the method called Atbash, that is a substitution of lau for aleph, shin for beth , and so on. The word is, however, no part of the original text of Jeremiah, being a conceit of later editors. In both passages it is lacking in LXX. [Note: Septuagint.] Cf. Leb-kamai.

J. F. McCurdy.

Smith's Bible Dictionary [4]

She'shach. ( from the goddess, Shach , Reduplicated). Sheshach is a term which occurs only in  Jeremiah 25:26;  Jeremiah 51:41, where it is, evidently, used as a synonym, for either Babylon or Babylonia.

American Tract Society Bible Dictionary [5]

A poetical name for Babylon, signifying, as some judge, house or court of the prince,  Jeremiah 25:26;  51:41 .

Holman Bible Dictionary [6]

 Jeremiah 25:26 Jeremiah 51:41 a z b y

Easton's Bible Dictionary [7]

 Jeremiah 25:26 Jeremiah 51:41

Cyclopedia of Biblical, Theological and Ecclesiastical Literature [8]

(Heb. Seshak', שֵׁשִׁךְ , probably an artificial word; Sept. Σεσάκ v.r. Σησάχ ), a term occurring only in Jeremiah (25:26; 51:41) who evidently uses it as a synonym either for Babylon or for Babylonia. According to the Jewish interpreters, followed by Jerome, it represents בבל , "Babel, " on a Cabalistic principle called "Athbash" well known to the later Jews the substitution of letters according to their position in the alphabet, counting backwards from the last letter, for those which hold the same numerical position counting in the ordinary way. (See Cabala). Thus ת represents א , שׁ represents ב , ר represents ג , and so on. It may well be doubted, however, whether this fanciful practice were as old as Jeremiah's time; and even supposing that were the case, why should he use this obscure term here, when Babylon is called by its proper name in the same verse? C.B. Michaelis conjectures that שׁש ׁ comes from שׁבשׁ , Shikshak, "to overlay with iron or other plates, "so that it might designate Babylon as Χαλκόπυλος . Von Bohlen thinks the word synonymous with the Persian Shih-shah, i.e. "house of the prince;" but it is doubtful whether, at so early a period as the age of Jeremiah, Babylon could have received a Persian name that would be known in Judea. Sir H. Rawlinson has observed that the name of the moon god, which was identical, or nearly so, with that of the city of Abraham Ur (or Hur), "might have been read in one of the ancient dialects of Babylon as Shishaki, " and that consequently "a possible explanation is thus obtained of the Sheshach of Scripture" (Herod. 1, 616). Shesach may stand for Ur; Ur itself, the old capital, being taken (as Babel, the new capital, constantly was) to represent the country.

International Standard Bible Encyclopedia [9]

shē´shak ( שׁשׁך , shēshakh , as if "humiliation"; compare שׁכך , shākhakh , "to crouch"): The general explanation is that this is "a cypherform of 'Babel' (Babylon)" which is the word given as equivalent to "Sheshach" by the Targum (  Jeremiah 25:26;  Jeremiah 51:41; the Septuagint omits in both passages). By the device known as Atbaš (אתבשׂ ), i.e. disguising a name by substituting the last letter of the alphabet for the first, the letter next to the last for the second, etc., ששך is substituted for שבבל , bābhel . This theory has not failed of opposition. Delitzsch holds that "Sheshach" represents Šiš - - KI of an old Babylonian regal register, which may have stood for a part of the city of Babylon. (For a refutation of this interpretation see Schrader, KAT2 , 415; COT , II, 108 f.) Lauth, too, takes "Sheshach" to be a Hebraization of Siska, a Babylonian district. Winckler and Sayce read Uru - azagga . Finally, Cheyne and a number of critics hold that the word has crept into the text, being "a conceit of later editors." See further Jeremiah , 6.

Kitto's Popular Cyclopedia of Biblial Literature [10]

She´shach, a name twice given by Jeremiah to Babylon . Its etymology and proper signification are doubtful.