The meaning of Merathaim in the Bible
(From International Standard Bible Encyclopedia)

mer-a-tha'-im (merathayim "double rebellion"): A name used for Babylon in Jeremiah 50:21. According to Delitzsch it may be equivalent to the Babylonian Marratun, i.e. land by the nar Marratu, "the bitter river" (Persian Gulf) = Southern Babylonia (OHL, under the word).

See more on the meaning of Merathaim in the Bible:
Merathaim {Easton's Bible Dictionary}

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