Green’s Dictionary of Slang

a shirt, coat or waistcoat.

1839		H. Brandon Dict. of the Flash or Cant Lang. 165/1: Shaker – a shirt.
1840		‘Monmouth Street’ in Lover’s Harmony No. 19 148: For thrums you’ll get a new bandana, / And a bran new shaker for a tanner.
1845		J. Lindridge Sixteen-String Jack 157: Off with your shakers, and toss on mine [...] Come, off with that coat, and waistcoat, and put on mine.
1859, 1860		Hotten Dict. of Modern Sl. etc.
1874		Derbyshire Courier 12 Dec. 7/1: Local Flash language [...] A shaker, a shirt.
1890–1904		Farmer & Henley Sl. and Its Analogues.