The Collaborative International Dictionary of English v.0.48:

Contingency \Con*tin"gen*cy\, n.; pl. Contingencies. [Cf. F.
   contingence.]
   1. Union or connection; the state of touching or contact.
      "Point of contingency." --J. Gregory.
      [1913 Webster]

   2. The quality or state of being contingent or casual; the
      possibility of coming to pass.
      [1913 Webster]

            Aristotle says we are not to build certain rules on
            the contingency of human actions.     --South.
      [1913 Webster]

   3. An event which may or may not occur; that which is
      possible or probable; a fortuitous event; a chance.
      [1913 Webster]

            The remarkable position of the queen rendering her
            death a most important contingency.   --Hallam.
      [1913 Webster]

   4. An adjunct or accessory. --Wordsworth.
      [1913 Webster]

   5. (Law) A certain possible event that may or may not happen,
      by which, when happening, some particular title may be
      affected.

   Syn: Casualty; accident; chance.
        [1913 Webster]

WordNet (r) 3.0 (2006):

contingency
    n 1: a possible event or occurrence or result [syn:
         eventuality, contingency, contingence]
    2: the state of being contingent on something

Moby Thesaurus II by Grady Ward, 1.0:

115 Moby Thesaurus words for "contingency":
   accessory, accident, accidental, addendum, addition, adjunct,
   adventure, appendage, appurtenance, aptitude, aptness, auxiliary,
   bare possibility, blind bargain, borderline case, break, casualty,
   chance, chance hit, circumstance, collateral, coming to be,
   conceivability, conceivableness, condition, conjuncture,
   contingent, correlation, crisis, crossroads, dependence,
   double contingency, emergency, even chance, event, eventuality,
   eventuation, exigency, extra, fluke, fortuity, freak accident,
   gamble, good chance, good possibility, guess, hap, happening,
   happenstance, hazard, hope, incidence, incident, incidental,
   inessential, interrelation, juncture, liability, liableness,
   likelihood, likeliness, long odds, long shot, lucky shot,
   materialization, mere chance, nonessential, not-self, obligation,
   occasion, occurrence, off chance, open question, opportunity,
   other, outside chance, outside hope, pass, piece of guesswork,
   pinch, possibility, possibleness, potential, potentiality,
   probability, proneness, prospect, question, realization,
   relativity, remote possibility, secondary,
   sight-unseen transaction, small hope, strait, subsidiary,
   superaddition, supplement, the attainable, the feasible,
   the possible, thinkability, thinkableness, toss-up, touch and go,
   turning point, undecided issue, unessential, virtuality, wager,
   weakness, what is possible, what may be, what might be,
   zero hour