The Collaborative International Dictionary of English v.0.48:

Debilitate \De*bil"i*tate\, v. t. [imp. & p. p. Debilitated;
   p. pr. & vb. n. Debilitating.] [L. debilitatus, p. p. of
   debilitare to debilitate, fr. debilis. See Debility.]
   To impair the strength of; to weaken; to enfeeble; as, to
   debilitate the body by intemperance.
   [1913 Webster]

         Various ails debilitate the mind.        --Jenyns.
   [1913 Webster]

         The debilitated frame of Mr. Bertram was exhausted by
         this last effort.                        --Sir W.
                                                  Scott.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

debilitating \debilitating\ adj.
   causing weakness. Opposite of invigorating.
   [WordNet 1.5]

WordNet (r) 3.0 (2006):

debilitating
    adj 1: impairing the strength and vitality [ant: invigorating]