Tashmitum appears as a goddess in the time of Hammurabi.  She is the consort of Nabu (q.v.)  Originally the consort of Nabu was Erua.  When Erua was amalgamated with Sarpanitum (q.v.) and assigned to Marduk (q.v.), a new consort had to be found for Nabu.  She is always coupled with Nabu ("Nabu and Tashmitum"), and never appears alone.  Jastrow thinks that originally the name was a title given to Nabu.  It was afterwards converted into a goddess. (An Encyclopedia of Religions, Canney, 1921)