Two little used and great descriptive words:

phthisis (pronounced alternately: tisis, tesis, thisis, and thesis; from Greek: phth- a wasting) obsolete medical term for consumption, most typically tuberculosis. A wasted (consumed) person is phthisic

Note: I prefer the thi sounding pronunciation for the noun, but the hard t for the adjective (my own strangeness). Also, I have seen it spelled with a y instead of the i, but both Dorlands and Stedmans medical dictionaries list it with the i. I have also (old medical journals/articles) seen the adjective spelled phthitic and phthytic.

Another favorite of mine:

wizened (wiz end; Old English wisnian to dry up) to dry up, wither, or shrivel

Thus a very sickly person can be described (I love documenting this in the charts and few people have any idea what I am saying) as: phthisic and wizened so much more colorful than wasted and dehydrated!!

Same root/meaning as phthisis leads to two other lovely words:

phthisiophobic intense, morbid fear of tuberculosis

phthisiotherapeutic of or related to the treatment of tuberculosis