Green’s Dictionary of Slang

1. washing day [the washing is ‘hanged’ out to dry].

c.1698		B.E. Dict. Canting Crew.
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue.
1811		Lex. Balatronicum.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.

2. (US) Monday; also the trad. washday.

1931

Irwin Amer. Tramp and Und. Sl. 69: Execution Day.–Monday, when the washing is ‘hung.’.