The Collaborative International Dictionary of English v.0.48:

Amsterdam \Amsterdam\ prop. n. (Geography)
   A large city which is an industrial center and the official
   capital of The Netherlands. Population (2000) = 724,096.

   Syn: Dutch capital, capital of The Netherlands
        [WordNet 1.5 +PJC]

WordNet (r) 3.0 (2006):

Amsterdam
    n 1: an industrial center and the nominal capital of the
         Netherlands; center of the diamond-cutting industry; seat
         of an important stock exchange; known for its canals and
         art museum [syn: Amsterdam, Dutch capital, capital of
         The Netherlands]