Green’s Dictionary of Slang

a thin person.

c.1597		Shakespeare Henry IV Pt 1 II iv: Here comes lean Jack, here comes bare-bone.
[1641		J. Taylor New Preachers [title] The disorderly preachment, pratings, and pratling of Mr. Barebones the Leather-seller, and Mr. Greene the Feltmaker].
1868		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.
1915		M.G. Hayden ‘Terms Of Disparagement’ in DN IV:iii 206: bare-bones, a skinny person. ‘Old bare-bones went gangling down the street.’.