The Collaborative International Dictionary of English v.0.48:

Organization \Or`gan*i*za"tion\
   ([^o]r`gan*[imac]*z[=a]"sh[u^]n), n. [Cf. F. organisation.]
   [1913 Webster]
   1. The act of organizing; the act of arranging in a
      systematic way for use or action; as, the organization of
      an army, or of a deliberative body. "The first
      organization of the general government." --Pickering.
      [1913 Webster]

   2. The state of being organized.
      [1913 Webster]

   3. That which is organized; an organized existence; an
      organism; specif. (Biol.), an arrangement of parts for the
      performance of the functions necessary to life.
      [1913 Webster]

            The cell may be regarded as the most simple, the
            most common, and the earliest form of organization.
                                                  --McKendrick.
      [1913 Webster]

   4. Specifically: A group of persons associated together for a
      common purpose and having a set of rules which specify the
      relations of the individual members to the whole gorup.
      [PJC]

   5. The manner in which something is organized; the relations
      included in an organized state or condition; as, the
      organization of the department permits ad hoc groups to
      form.
      [PJC]

            What is organization but the connection of parts in
            and for a whole, so that each part is, at once, end
            and means?                            --Coleridge.
      [1913 Webster]

WordNet (r) 3.0 (2006):

organization
    n 1: a group of people who work together [syn: organization,
         organisation]
    2: an organized structure for arranging or classifying; "he
       changed the arrangement of the topics"; "the facts were
       familiar but it was in the organization of them that he was
       original"; "he tried to understand their system of
       classification" [syn: arrangement, organization,
       organisation, system]
    3: the persons (or committees or departments etc.) who make up a
       body for the purpose of administering something; "he claims
       that the present administration is corrupt"; "the governance
       of an association is responsible to its members"; "he quickly
       became recognized as a member of the establishment" [syn:
       administration, governance, governing body,
       establishment, brass, organization, organisation]
    4: the act of organizing a business or an activity related to a
       business; "he was brought in to supervise the organization of
       a new department" [syn: organization, organisation]
    5: an ordered manner; orderliness by virtue of being methodical
       and well organized; "his compulsive organization was not an
       endearing quality"; "we can't do it unless we establish some
       system around here" [syn: organization, organisation,
       system]
    6: the activity or result of distributing or disposing persons
       or things properly or methodically; "his organization of the
       work force was very efficient" [syn: organization,
       organisation]
    7: the act of forming or establishing something; "the
       constitution of a PTA group last year"; "it was the
       establishment of his reputation"; "he still remembers the
       organization of the club" [syn: constitution,
       establishment, formation, organization, organisation]

Moby Thesaurus II by Grady Ward, 1.0:

276 Moby Thesaurus words for "organization":
   KP, adjustment, aerobic organism, affiliation, agency,
   anaerobic organism, anatomy, approach, architectonics,
   architecture, army, army group, arrangement, array, assemblage,
   assembling, assembly, atelier, attack, autotrophic organism,
   barbershop, battalion, battery, battle group, beauty parlor,
   beauty shop, being, bench, blueprint, blueprinting, body, branch,
   brigade, build, building, buildup, butcher shop, cadre,
   calculation, categorization, categorizing, charting, church,
   classification, classifying, coalition, codification, codifying,
   cohort, column, combat command, combat team, combination, combine,
   communion, community, company, composition, compound, conception,
   concern, concord, confederacy, confederation, configuration,
   conformation, conglomerate, consortium, constitution, construction,
   contrivance, coordination, corporation, corps, creation, creature,
   denomination, deployment, design, desk, detachment, detail, device,
   disposal, disposition, division, effectuation, embodiment,
   enterprise, envisagement, establishment, fabric, fabrication,
   facility, faction, fashion, fashioning, federation, fellowship,
   field army, field train, figuring, file, firm, flying column,
   foresight, forethought, forging, form, format, formation,
   foundation, frame, framework, game, garrison, genetic individual,
   getup, graphing, ground plan, group, grouping, guidelines,
   harmonization, harmony, heterotrophic organism, house, idea,
   inauguration, inception, incorporation, individual, installation,
   institute, institution, intention, junction, kitchen police,
   layout, league, legion, lineup, living being, living thing, loft,
   long-range plan, make, makeup, making, maniple, manufacture,
   mapping, marshaling, master plan, materialization, method,
   methodization, methodology, microbe, microorganism, mixture, mold,
   molding, morphological individual, normalization, offshoot, ont,
   operations research, order, ordination, organic being,
   organic structure, organism, organizing, outfit, parlor, party,
   pattern, patterning, peace, persuasion, phalanx,
   physiological individual, physique, piecing together, plan,
   planning, planning function, platoon, posse, prearrangement,
   procedure, production, program, program of action, proportion,
   putting together, quiet, quietude, rank, rationalization,
   realization, regiment, regularity, regularization, regulation,
   religious order, routine, routinization, schedule, schema,
   schematism, schematization, scheme, scheme of arrangement, schism,
   school, sect, sectarism, section, segment, setting-up, setup,
   shape, shaping, shop, society, squad, squadron, strategic plan,
   strategy, structure, structuring, studio, sweatshop, symmetry,
   syndicate, syneresis, synthesis, system, systematization,
   systematizing, tactical plan, tactical unit, tactics, task force,
   tectonics, texture, the big picture, the picture, tissue, train,
   tranquillity, troop, uniformity, unit, variety, version, virus,
   warp and woof, way, weave, web, wing, work site, work space,
   workbench, workhouse, working plan, working space, workplace,
   workroom, workshop, worktable, zooid, zoon