The Collaborative International Dictionary of English v.0.48:

Damnable \Dam"na*ble\, a. [L. damnabilis, fr. damnare: cf. F.
   damnable. See Damn.]
   1. Liable to damnation; deserving, or for which one deserves,
      to be damned; of a damning nature.
      [1913 Webster]

            A creature unprepared unmeet for death,
            And to transport him in the mind he is,
            Were damnable.                        --Shak.
      [1913 Webster]

   2. Odious; pernicious; detestable.
      [1913 Webster]

            Begin, murderer; . . . leave thy damnable faces.
                                                  --Shak.
      [1913 Webster]

WordNet (r) 3.0 (2006):

damnable
    adj 1: deserving a curse; "her damnable pride" [syn: damnable,
           execrable]