The Collaborative International Dictionary of English v.0.48:

Likelihood \Like"li*hood\ (l[imac]k"l[i^]*h[oo^]d), n. [Likely +
   -hood.]
   1. Appearance; show; sign; expression. [Obs.]
      [1913 Webster]

            What of his heart perceive you in his face
            By any likelihood he showed to-day ?  --Shak.
      [1913 Webster]

   2. Likeness; resemblance. [Obs.]
      [1913 Webster]

            There is no likelihood between pure light and black
            darkness, or between righteousness and reprobation.
                                                  --Sir W.
                                                  Raleigh.
      [1913 Webster]

   3. Appearance of truth or reality; probability;
      verisimilitude. --Tennyson.
      [1913 Webster]

   4. Statistical probability; probability of being true or of
      occurring in the future; as, the likelihood of being
      abducted by aliens is close to zero..
      [PJC]

WordNet (r) 3.0 (2006):

likelihood
    n 1: the probability of a specified outcome [syn: likelihood,
         likeliness] [ant: unlikelihood, unlikeliness]

Moby Thesaurus II by Grady Ward, 1.0:

62 Moby Thesaurus words for "likelihood":
   aptitude, aptness, bare possibility, best bet, chance,
   conceivability, conceivableness, contingency, even chance,
   eventuality, expectation, expectations, fair expectation,
   favorable prospect, good chance, good opportunity,
   good possibility, hope, hopes, liability, liableness, likeliness,
   main chance, obligation, odds, odds-on, odds-on chance, off chance,
   outlook, outside chance, outside hope, possibility, possibleness,
   potential, potentiality, presumption, presumptive evidence,
   probabilism, probability, proneness, prospect, prospects,
   reasonable ground, reasonable hope, remote possibility, small hope,
   sporting chance, sure bet, sure thing, tendency, the attainable,
   the feasible, the possible, thinkability, thinkableness,
   verisimilitude, virtuality, weakness, well-grounded hope,
   what is possible, what may be, what might be