Merathaim
MERATHAIM (mĕr-a-thā'ĭm, repeated rebellion). A symbolic name for Babylon, used by Jeremiah (Jer.50.21) in his “doom of Babylon” in Jer.50.1-Jer.50.46-Jer.51.1-Jer.51.64.
MERATHAIM mĕr’ ə thā’ əm (מְרָתַ֨יִם). A symbolic name for Babylon in Jeremiah 50:21. Here it is used as a play on words, RSV meaning “double rebellion.” The name Marratim, a region in S Babylonia, may have suggested this use.
International Standard Bible Encyclopedia (1915)
A name used for Babylon in Jer 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).