The Collaborative International Dictionary of English v.0.48:

Decision \De*ci"sion\, n. [L. decisio, fr. dec[imac]dere,
   decisum: cf. F. d['e]cision. See Decide.]
   1. Cutting off; division; detachment of a part. [Obs.] --Bp.
      Pearson.
      [1913 Webster]

   2. The act of deciding; act of settling or terminating, as a
      controversy, by giving judgment on the matter at issue;
      determination, as of a question or doubt; settlement;
      conclusion.
      [1913 Webster]

            The decision of some dispute.         --Atterbury.
      [1913 Webster]

   3. An account or report of a conclusion, especially of a
      legal adjudication or judicial determination of a question
      or cause; as, a decision of arbitrators; a decision of the
      Supreme Court.
      [1913 Webster]

   4. The quality of being decided; prompt and fixed
      determination; unwavering firmness; as, to manifest great
      decision.

   Syn: Decision, Determination, Resolution.

   Usage: Each of these words has two meanings, one implying the
          act of deciding, determining, or resolving; and the
          other a habit of mind as to doing. It is in the last
          sense that the words are here compared. Decision is a
          cutting short. It implies that several courses of
          action have been presented to the mind, and that the
          choice is now finally made. It supposes, therefore, a
          union of promptitude and energy. Determination is the
          natural consequence of decision. It is the settling of
          a thing with a fixed purpose to adhere. Resolution is
          the necessary result in a mind which is characterized
          by firmness. It is a spirit which scatters (resolves)
          all doubt, and is ready to face danger or suffering in
          carrying out one's determinations. Martin Luther was
          equally distinguished for his prompt decision, his
          steadfast determination, and his inflexible
          resolution.
          [1913 Webster]

WordNet (r) 3.0 (2006):

decision
    n 1: the act of making up your mind about something; "the burden
         of decision was his"; "he drew his conclusions quickly"
         [syn: decision, determination, conclusion]
    2: a position or opinion or judgment reached after
       consideration; "a decision unfavorable to the opposition";
       "his conclusion took the evidence into account"; "satisfied
       with the panel's determination" [syn: decision,
       determination, conclusion]
    3: (boxing) a victory won on points when no knockout has
       occurred; "had little trouble in taking a unanimous decision
       over his opponent"
    4: the outcome of a game or contest; "the team dropped three
       decisions in a row"
    5: the trait of resoluteness as evidenced by firmness of
       character or purpose; "a man of unusual decisiveness" [syn:
       decisiveness, decision] [ant: indecision,
       indecisiveness]

Moby Thesaurus II by Grady Ward, 1.0:

109 Moby Thesaurus words for "decision":
   accommodation, accord, acquittal, action, adjustment, agreement,
   alternativity, animus, appetence, appetency, appetite, arbitration,
   arrangement, award, backbone, choice, choosing, co-optation,
   co-option, command, commitment, compromise, conation, conatus,
   conclusion, condemnation, consideration, decidedness, decisiveness,
   decree, dedication, definiteness, deliverance, desire,
   determinateness, determination, determinedness, devotion,
   diagnosis, dictum, discretion, disposition, doggedness, doom,
   earnestness, election, fancy, finding, firmness, first choice,
   fortitude, free choice, free will, grit, inclination, intention,
   judgement, judgment, landmark decision, liking, lust, mind,
   objective, obstinacy, order, outcome, passion, penalty,
   perseverance, persistence, pick, pleasure, pluck, precedent,
   preference, preoption, prognosis, pronouncement, purpose,
   purposefulness, reconciliation, relentlessness, resoluteness,
   resolution, resolve, resolvedness, resolving, ruling, selection,
   self-will, sentence, seriousness, settlement, settling,
   sexual desire, sincerity, single-mindedness, steadfastness,
   stubbornness, tenacity, the pick, total commitment, understanding,
   velleity, verdict, volition, will, will power, wish



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

DECISION, practice. A judgment given by a competent tribunal. The French
lawyers call the opinions which they give on questions propounded to them,
decisions. Vide Inst. 1, 2, 8 Dig. 1, 2, 2.