WordNet (r) 3.0 (2006):

city hall
    n 1: a building that houses administrative offices of a
         municipal government

Moby Thesaurus II by Grady Ward, 1.0:

56 Moby Thesaurus words for "city hall":
   American Party, Anti-Monopoly Party, Bull Moose Party,
   Communist Party, Conservative Party, Constitutional Union Party,
   Democratic Party, Democratic-Republican Party, Farmer-Labor Party,
   Federalist Party, Free Soil Party, Greenback Party,
   Know-Nothing Party, Labour Party, Liberal Party,
   Liberal Republican Party, Liberty Party, National Republican Party,
   Populist Party, Progressive Party, Prohibition Party,
   Republican Party, Socialist Labor Party, Socialist Party,
   Socialist Workers Party, Tammany Hall, Tory Party, Whig Party,
   camp, capitol, community center, county building,
   county courthouse, courthouse, faction, fire station, firehouse,
   machine, major party, minor party, multiple party system,
   municipal building, one-party system, opposition party, party,
   party in power, police headquarters, police station,
   political machine, political party, precinct house, splinter party,
   statehouse, third party, town hall, two-party system