The Collaborative International Dictionary of English v.0.48:

Accountable \Ac*count"a*ble\, a.
   1. Liable to be called on to render an account; answerable;
      as, every man is accountable to God for his conduct.
      [1913 Webster]

   2. Capable of being accounted for; explicable. [R.]
      [1913 Webster]

            True religion . . . intelligible, rational, and
            accountable, -- not a burden but a privilege. --B.
                                                  Whichcote.
      [1913 Webster]

   Syn: Amenable; responsible; liable; answerable.
        [1913 Webster]

WordNet (r) 3.0 (2006):

accountable
    adj 1: liable to account for one's actions; "governments must be
           accountable to someone beside themselves"; "fully
           accountable for what they did"; "the court held the
           parents answerable for their minor child's acts of
           vandalism"; "he was answerable to no one"

Moby Thesaurus II by Grady Ward, 1.0:

36 Moby Thesaurus words for "accountable":
   Englishable, alleged, amenable, answerable, ascribable, assignable,
   attributable, attributed, chargeable, charged, construable,
   credited, definable, derivable from, derivational, derivative,
   describable, due, explainable, explicable, imputable, imputed,
   interpretable, liable, obligated, obliged, owing, putative,
   referable, referred to, renderable, responsible, responsible for,
   to blame, traceable, translatable