Green’s Dictionary of Slang

shroud n.

(US) a formal dress suit.

[US] ‘Jargon of the Und.’ in DN V 462: Shroud, A suit of clothes.
[US]Irwin Amer. Tramp and Und. Sl. 169: Shroud. – A suit of clothes.
[US]Monteleone Criminal Sl. (rev. edn) 208: shroud A suit of clothes.

In compounds

shroud and boiler (n.)

(US) a formal dress suit and starched dress shirt.

[US]H. Green Maison De Shine 138: I’m there wit’ the old shroud and boiler [...] We oughta fix up. It’s a first night.
[US]Eve. World (NY) 21 Mar. 10/6: ‘Now I’ve got this shroud and boiler on I’m going [to] learn the tango.