The Collaborative International Dictionary of English v.0.48:

Porte \Porte\, n. [F. porte a gate, L. porta. See Port a
   gate.]
   The Ottoman court; the government of the Turkish empire,
   officially called the Sublime Porte, from the gate (port)
   of the sultan's palace at which justice was administered.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Sublime Porte
    n 1: the Ottoman court in Constantinople [syn: Porte, Sublime
         Porte]