late 14c., "at the coming of the Lord," a Bible word, from Greek maranatha, a Greek form of an untranslated Aramaic (Semitic) word in I Corinthians xvi.22, where it follows Greek anathema (with which it has no grammatical connection), and therefore has been taken as part of a phrase which is used as a curse (see anathema). The Aramaic word has been explained as "Our Lord, come thou" or "Our Lord hath come," apparently a solemn formula of confirmation, like amen; but possibly it is a false transliteration of Hebrew mohoram atta "you are put under the ban," which would make sense in the context [Klein].
1520s, "an accursed thing," from Latin anathema "an excommunicated person; the curse of excommunication," from Ecclesiastical Greek anathema "a thing accursed," a slight variation of classical Greek anathāma, which meant merely "a thing devoted," literally "a thing set up (to the gods)," such as a votive offering in a temple, from ana "up" (see ana-) + tithenai "to put, to place," from reduplicated form of PIE root *dhe- "to set, put."
By the time it reached Late Latin the meaning of the Greek word had progressed through "thing devoted to evil," to "thing accursed or damned." Later it was applied to persons and the Divine Curse. Meaning "act or formula of excommunicating and consigning to damnation by ecclesiastical authority" is from 1610s.
Anathema maranatha, taken as an intensified form, is held to be a misreading of I Corinthians xvi.22 where anathema is followed by Aramaic maran atha "Our Lord hath come" (see Maranatha).