The Collaborative International Dictionary of English v.0.48:

Culpable \Cul"pa*ble\ (k?l"p?-b'l), a. [OE. culpable, coulpable,
   coupable, F. coupable, formerly also coupable, formerly also
   coulpable, culpable, fr. L. culpabilis, fr. culpare to blame,
   fr. culpa fault.]
   [1913 Webster]
   1. Deserving censure; worthy of blame; faulty; immoral;
      criminal. --State Trials (1413).
      [1913 Webster]

            If he acts according to the best reason he hath, he
            is not culpable, though he be mistaken in his
            measures.                             --Sharp.
      [1913 Webster]

   2. Guilty; as, culpable of a crime. [Obs.] --Spenser. --
      Cul"pa*ble*ness, n. -- Cul"pa*bly, adv.
      [1913 Webster]

WordNet (r) 3.0 (2006):

culpable
    adj 1: deserving blame or censure as being wrong or evil or
           injurious; "blameworthy if not criminal behavior";
           "censurable misconduct"; "culpable negligence" [syn:
           blameworthy, blamable, blameable, blameful,
           censurable, culpable]

Moby Thesaurus II by Grady Ward, 1.0:

26 Moby Thesaurus words for "culpable":
   accusable, amiss, arraignable, at fault, blamable, blameful,
   blameworthy, censurable, chargeable, criminal, faulty, guilty,
   impeachable, implicated, imputable, inculpated, indictable,
   involved, open to criticism, peccant, reprehensible, reproachable,
   reprovable, sinful, to blame, unholy