WordNet (r) 3.0 (2006):

Forbidden City
    n 1: the sacred city of Lamaism; known as the Forbidden City for
         its former inaccessibility and hostility to strangers [syn:
         Lhasa, Lassa, capital of Tibet, Forbidden City]
    2: a walled section of Beijing that encloses the palace that was
       formerly the residence of the emperor of China