The Collaborative International Dictionary of English v.0.48:

phthisis \phthi"sis\ (th[imac]"s[i^]s; 277), n. [L., fr. Gr.
   fqi`sis, fr. fqi`ein to pass or waste away: cf. F. phthisie.]
   (Med.)
   A wasting or consumption of the tissues. The term is now
   obsolete; it was once applied to many wasting diseases, but
   in the early 1900's became restricted to tuberculosis of the
   lungs (pulmonary phthisis, or consumption). See
   Consumption. [Obs.]
   [1913 Webster + PJC]

   Fibroid phthisis. See under Fibroid.
      [1913 Webster]

WordNet (r) 3.0 (2006):

phthisis
    n 1: involving the lungs with progressive wasting of the body
         [syn: pulmonary tuberculosis, consumption, phthisis,
         wasting disease, white plague]