What is the term meaning abnormally thin?

Answer 1

Cachectic - Having cachexia, physical wasting with loss of weight and muscle mass due to disease. Patients with advanced cancer, AIDS, and some other major chronic progressive diseases may appear cachectic.
emaciated and gaunt come to mind

Answer 2

Osteopenia is a condition where bone mineral density is lower than normal. It is considered by many doctors to be a precursor to osteoporosis. However, not every person diagnosed with osteopenia will develop osteoporosis. More specifically, osteopenia is defined as a bone mineral density T score between -1.0 and -2.5. (Source Wikipedia)

Osteopenia, "osteo-" means bone, and "-penia" means deficient in quantity.
Osteopenia is a condition where bone mineral density is lower than normal. It is considered by many doctors to be a precursor to osteoporosis. However, not every person diagnosed with osteopenia will develop osteoporosis. More specifically, osteopenia is defined as a bone mineral density T score between -1.0 and -2.5. (Source Wikipedia)

Osteopenia, "osteo-" means bone, and "-penia" means deficient in quantity.

Answer 3

emaciation

Answer 4

emaciated

Answer 5

Anorexic.