The Collaborative International Dictionary of English v.0.48:

Town \Town\ (toun), n. [OE. toun, tun, AS. tun inclosure, fence,
   village, town; akin to D. tuin a garden, G. zaun a hadge,
   fence, OHG. zun, Icel. tun an inclosure, homestead, house,
   Ir. & Gael. dun a fortress, W. din. Cf. Down, adv. & prep.,
   Dune, tine to inclose.]
   1. Formerly:
      (a) An inclosure which surrounded the mere homestead or
          dwelling of the lord of the manor. [Obs.]
      (b) The whole of the land which constituted the domain.
          [Obs.]
      (c) A collection of houses inclosed by fences or walls.
          [Obs.] --Palsgrave.
          [1913 Webster]

   2. Any number or collection of houses to which belongs a
      regular market, and which is not a city or the see of a
      bishop. [Eng.] --Johnson.
      [1913 Webster]

   3. Any collection of houses larger than a village, and not
      incorporated as a city; also, loosely, any large, closely
      populated place, whether incorporated or not, in
      distinction from the country, or from rural communities.
      [1913 Webster]

            God made the country, and man made the town.
                                                  --Cowper.
      [1913 Webster]

   4. The body of inhabitants resident in a town; as, the town
      voted to send two representatives to the legislature; the
      town voted to lay a tax for repairing the highways.
      [1913 Webster]

   5. A township; the whole territory within certain limits,
      less than those of a country. [U. S.]
      [1913 Webster]

   6. The court end of London; -- commonly with the.
      [1913 Webster]

   7. The metropolis or its inhabitants; as, in winter the
      gentleman lives in town; in summer, in the country.
      [1913 Webster]

            Always hankering after the diversions of the town.
                                                  --Addison.
      [1913 Webster]

            Stunned with his giddy larum half the town. --Pope.
      [1913 Webster]

   Note: The same form of expressions is used in regard to other
         populous towns.
         [1913 Webster]

   8. A farm or farmstead; also, a court or farmyard. [Prov.
      Eng. & Scot.]
      [1913 Webster]

   Note: Town is often used adjectively or in combination with
         other words; as, town clerk, or town-clerk; town-crier,
         or town crier; townhall, town-hall, or town hall;
         townhouse, town house, or town-house.
         [1913 Webster]

   Syn: Village; hamlet. See Village.
        [1913 Webster]

   Town clerk, an office who keeps the records of a town, and
      enters its official proceedings. See Clerk.

   Town cress (Bot.), the garden cress, or peppergrass. --Dr.
      Prior.

   Town house.
      (a) A house in town, in distinction from a house in the
          country.
      (b) See Townhouse.

   Town meeting, a legal meeting of the inhabitants of a town
      entitled to vote, for the transaction of public bisiness.
      [U. S.]

   Town talk, the common talk of a place; the subject or topic
      of common conversation.
      [1913 Webster]

WordNet (r) 3.0 (2006):

town
    n 1: an urban area with a fixed boundary that is smaller than a
         city; "they drive through town on their way to work"
    2: the people living in a municipality smaller than a city; "the
       whole town cheered the team" [syn: town, townspeople,
       townsfolk]
    3: an administrative division of a county; "the town is
       responsible for snow removal" [syn: township, town]
    4: United States architect who was noted for his design and
       construction of truss bridges (1784-1844) [syn: Town,
       Ithiel Town]

Moby Thesaurus II by Grady Ward, 1.0:

60 Moby Thesaurus words for "town":
   Kreis, archbishopric, archdiocese, arrondissement, bailiwick,
   bishopric, borough, burgh, burghal, canton, citified, city, civic,
   commune, community, congressional district, constablewick, county,
   departement, diocese, district, downtown, duchy,
   electoral district, electorate, government, hamlet, hundred,
   interurban, magistracy, metropolis, metropolitan,
   metropolitan area, midtown, municipal, municipality, oblast, okrug,
   oppidan, parish, precinct, principality, province, region, riding,
   sheriffalty, sheriffwick, shire, shrievalty, soke, stake, state,
   suburban, territory, township, uptown, urban, village, wapentake,
   ward



Bouvier's Law Dictionary, Revised 6th Ed (1856):

TOWN. This word is used differently in different parts of the United States.
In Pennsylvania and some other of the middle states, it signifies a village
or a city. In some of the northeastern states it denotes a subdivision of a
county, called in other places a township.