Green’s Dictionary of Slang

shappo n.

a hat.

c.1698		B.E. Dict. Canting Crew n.p.: Shappeau, or Shappo, for Chappeau, a Hat, the newest Cant, Nab being very old, and grown too common.
1708		J. Hall Memoirs (1714) 13: Shap, a Hat.
1718		C. Hitchin Regulator 19: A Shap, alias Hatt.
1719		A. Smith Lives of Most Notorious Highway-men, etc. (1926) 209: Shappau, or Shappo for Chappeau, a Hat. (This is the newest cant, nab being very old, and grown too common).
1725		New Canting Dict. [as cit. 1719].
1737, 1759, 1760, 1776		Bailey Universal Etym. Eng. Dict. [as cit. 1719].
1741		Canting Academy, or the Pedlar’s-French Dict. 112: A Hat A Shappo.
1768		(con. 1710–25) Tyburn Chronicle II in Groom (1999) xxix: A Shap A Hat.
1785		Grose Classical Dict. of the Vulgar Tongue n.p.: Shappo, a hat, corruption of chapeau.
c.1786		Grose Classical Dict. of the Vulgar Tongue ms. additions n.p.: Shap, a Hat. Cant.
1796		Grose Classical Dict. of the Vulgar Tongue (3rd edn) n.p.: Shappo, or Shap. A hat: corruption of chapeau.
1811		Lex. Balatronicum [as cit. 1796].
1848		J.R. Lowell Biglow Papers (1880) 13: An’ th’ Cunnles, tu, could kiver up their shappoes with bandanners.
1856		Yorkville Enquirer (SC) 14 Feb. 4/3: ‘You ought ’t get a Spring Hat — a Shappoh Mechanic, as the French say’.
1859		Matsell Vocabulum 79: shap a Hat.
1862		‘Artemus Ward’ Artemus Ward, His Book 201: ‘My illustrious and patriotic Bummers!’ sez I, a gittin up and takin orf my Shappo.
1907		Sun. Times (Perth) 22 Sept. 4/7: ‘Take orf yer ’at,’ squealed Bill Lockhart [...] B.L. made the fatal error of trying to knock the said chapeaux off.