The Collaborative International Dictionary of English v.0.48:

Thebaic \The*ba"ic\, a. [L. thebaicus, Gr. ?.]
   Of or pertaining to Thebes in Egypt; specifically,
   designating a version of the Bible preserved by the Copts,
   and esteemed of great value by biblical scholars. This
   version is also called the Sahidic version.
   [1913 Webster]