Green’s Dictionary of Slang

barebones n.

also barebone

a thin person.

[UK]Shakespeare Henry IV Pt 1 II iv: Here comes lean Jack, here comes bare-bone.
[Aus]Rockhampton Bull. (Qld) 1 Oct. 3/2: It was but a simple and primitive socioety [...] when men caled each other Addlehead, Baldhead, Barebones, Bitch [...] Chisels, Dolt [...] Fogey [...] Gander [...] Maggot, Mangy, Muff, Muzzy.
[US]M.G. Hayden ‘Terms Of Disparagement’ in DN IV:iii 206: bare-bones, a skinny person. ‘Old bare-bones went gangling down the street.’.