The Collaborative International Dictionary of English v.0.48:

Solvability \Solv`a*bil"i*ty\, n. [F. solvabilit['e].]
   1. The quality or state of being solvable; as, the
      solvability of a difficulty; the solvability of a problem.
      [1913 Webster]

   2. The condition of being solvent; ability to pay all just
      debts; solvency; as, the solvability of a merchant.
      [1913 Webster]

WordNet (r) 3.0 (2006):

solvability
    n 1: the property (of a problem or difficulty) that makes it
         possible to solve [syn: solvability, solubility] [ant:
         insolubility, unsolvability]