The Collaborative International Dictionary of English v.0.48:

Dublin \Dublin\ prop. n. (Geography)
   The capital city of Ireland. Population (2000) = nk.
   [PJC]

WordNet (r) 3.0 (2006):

Dublin
    n 1: capital and largest city and major port of the Irish
         Republic [syn: Dublin, Irish capital, capital of
         Ireland]