Source : Webster's Revised Unabridged Dictionary (1913)

Abba \Ab"ba\ ([a^]b"b[.a]), n. [Syriac abb[=a] father. See
   {Abbot}.]
   Father; religious superior; -- in the Syriac, Coptic, and
   Ethiopic churches, a title given to the bishops, and by the
   bishops to the patriarch.