The Collaborative International Dictionary of English v.0.48:

Beijing \Beijing\ prop. n. (Geography)
   The capital city of China. Formerly called Peking.
   Population (2000) = 12,033,000.
   [PJC]

WordNet (r) 3.0 (2006):

Peking
    n 1: capital of the People's Republic of China in the Hebei
         province in northeastern China; 2nd largest Chinese city
         [syn: Beijing, Peking, Peiping, capital of Red
         China]