1
general::
Painfully thin, emaciated. This phrase often is expanded to nothing but skin and bones, as in She came home from her trip nothing but skin and bones. This hyperbolic expression? one could hardly be alive without some flesh? dates from the early 1400s.
American Heritage Idioms
2
general::
Phrase(s): (all) skin and bones
Go to nothing but skin and bones.
McGrawhill's American Idioms And Phrasal Verbs