Green’s Dictionary of Slang

rag n.2

[‘The familiar name of the Rag, by which it is generally known, was invented by Captain William Duff, of the 23rd Fusiliers. Coming in to supper late one night, the refreshment obtainable appeared so meagre that he nicknamed the club the Rag and Famish’ (Nevill & Jerningham, Piccadilly to Pall Mall, 1908); note also the less well-known Rag: the Raglan Music Hall in Leather Lane, off Holborn WC2]

[mid-19C+] an abbr. of the Rag and Famish, the Army and Navy Club, London.