The Collaborative International Dictionary of English v.0.48:

Imputable \Im*put"a*ble\, a. [Cf. F. imputable.]
   [1913 Webster]
   1. That may be imputed; capable of being imputed; chargeable;
      ascribable; attributable; referable.
      [1913 Webster]

            A prince whose political vices, at least, were
            imputable to mental incapacity.       --Prescott.
      [1913 Webster]

   2. Accusable; culpable. [R.]
      [1913 Webster]

            The fault lies at his door, and she is no wise
            imputable.                            --Ayliffe.
      [1913 Webster]

WordNet (r) 3.0 (2006):

imputable
    adj 1: capable of being assigned or credited to; "punctuation
           errors ascribable to careless proofreading"; "the
           cancellation of the concert was due to the rain"; "the
           oversight was not imputable to him" [syn: ascribable,
           due, imputable, referable]

Moby Thesaurus II by Grady Ward, 1.0:

33 Moby Thesaurus words for "imputable":
   accountable, accusable, alleged, arraignable, ascribable,
   assignable, attributable, attributed, blamable, blameworthy,
   censurable, chargeable, charged, credited, culpable,
   derivable from, derivational, derivative, due, explicable,
   impeachable, imputed, indictable, open to criticism, owing,
   putative, referable, referred to, reprehensible, reproachable,
   reprovable, to blame, traceable