The Collaborative International Dictionary of English v.0.48:

Commons \Com"mons\, n. pl.,
   1. The mass of the people, as distinguished from the titled
      classes or nobility; the commonalty; the common people.
      [Eng.]
      [1913 Webster]

            'T is like the commons, rude unpolished hinds,
            Could send such message to their sovereign. --Shak.
      [1913 Webster]

            The word commons in its present ordinary
            signification comprises all the people who are under
            the rank of peers.                    --Blackstone.
      [1913 Webster]

   2. The House of Commons, or lower house of the British
      Parliament, consisting of representatives elected by the
      qualified voters of counties, boroughs, and universities.
      [1913 Webster]

            It is agreed that the Commons were no part of the
            great council till some ages after the Conquest.
                                                  --Hume.
      [1913 Webster]

   3. Provisions; food; fare, -- as that provided at a common
      table in colleges and universities.
      [1913 Webster]

            Their commons, though but coarse, were nothing
            scant.                                --Dryden.
      [1913 Webster]

   4. A club or association for boarding at a common table, as
      in a college, the members sharing the expenses equally;
      as, to board in commons.
      [1913 Webster]

   5. A common; public pasture ground.
      [1913 Webster]

            To shake his ears, and graze in commons. --Shak.
      [1913 Webster]

   Doctors' Commons, a place near St. Paul's Churchyard in
      London where the doctors of civil law used to common
      together, and where were the ecclesiastical and admiralty
      courts and offices having jurisdiction of marriage
      licenses, divorces, registration of wills, etc.

   To be on short commons, to have a small allowance of food.
      [Colloq.]
      [1913 Webster] Common sense

WordNet (r) 3.0 (2006):

commons
    n 1: a piece of open land for recreational use in an urban area;
         "they went for a walk in the park" [syn: park, commons,
         common, green]
    2: a pasture subject to common use [syn: commons, common
       land]
    3: a class composed of persons lacking clerical or noble rank
       [syn: commonalty, commonality, commons]
    4: the common people [syn: third estate, Commons]

Moby Thesaurus II by Grady Ward, 1.0:

63 Moby Thesaurus words for "commons":
   C ration, K ration, allotment, allowance, board, bourgeoisie,
   cafeteria, common, common people, common run, common sort,
   commonage, commonality, commonalty, commoners, dinette, dining car,
   dining hall, dining room, dining saloon, emergency rations,
   field rations, laborers, linendrapers, lower classes,
   lower middle class, lower orders, lumpen proletariat, meals, mess,
   mess hall, messroom, middle class, middle orders, ordinary people,
   paradise, park, peasantry, plain folks, plain people, pleasance,
   pleasure garden, pleasure ground, proletariat, public park,
   rank and file, rations, refectory, restaurant, salle a manger,
   shopkeepers, short commons, small tradesmen, the lower cut,
   the other half, the third estate, toilers, toiling class, tucker,
   upper middle class, vulgus, working class, working people



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

COMMONS, Eng. law. Those subjects of the English nation who are not
noblemen. They are represented in parliament in the house of commons.