The Collaborative International Dictionary of English v.0.48:

Metropolis \Me*trop"o*lis\, n. [L. metropolis, Gr. ?, prop., the
   mother city (in relation to colonies); ? mother + ? city. See
   Mother, and Police.]
   [1913 Webster]
   1. The mother city; the chief city of a kingdom, state, or
      country.
      [1913 Webster]

            [Edinburgh] gray metropolis of the North.
                                                  --Tennyson.
      [1913 Webster]

   2. (Eccl.) The seat, or see, of the metropolitan, or highest
      church dignitary.
      [1913 Webster]

            The great metropolis and see of Rome. --Shak.
      [1913 Webster]

   3. Any large city.
      [PJC]

WordNet (r) 3.0 (2006):

metropolis
    n 1: a large and densely populated urban area; may include
         several independent administrative districts; "Ancient Troy
         was a great city" [syn: city, metropolis, urban
         center]
    2: people living in a large densely populated municipality; "the
       city voted for Republicans in 1994" [syn: city,
       metropolis]

The Devil's Dictionary (1881-1906):

METROPOLIS, n.  A stronghold of provincialism.