The Collaborative International Dictionary of English v.0.48:

Punishable \Pun"ish*a*ble\, a. [Cf. F. punissable.]
   Deserving of, or liable to, punishment; capable of being
   punished by law or right; -- said of person or offenses.
   [1913 Webster]

         That time was, when to be a Protestant, to be a
         Christian, was by law as punishable as to be a traitor.
                                                  -- Milton.
   [1913 Webster] -- Pun"ish*a*ble*ness, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

punishable
    adj 1: liable to or deserving punishment; "punishable offenses"
    2: subject to punishment by law; "a penal offense" [syn:
       penal, punishable]