Source : Webster's Revised Unabridged Dictionary (1913)

Apostolic delegate \Ap`os*tol"ic del"e*gate\ (R. C. Ch.)
   The diplomatic agent of the pope highest in grade, superior
   to a nuncio.

Source : WordNet®

apostolic delegate
     n : (Roman Catholic Church) a representative of the Holy See in
         a country that has no formal diplomatic relations with it