Quiz: Remember the definition of mal de mer?
1670s, "fall or sink into a muddy place," probably from a Scandinavian source, cf. Norwegian and Danish slumpe "fall upon," Swedish slumpa; perhaps ultimately of imitative origin. Related: Slumped; slumping.
The word "slump," or "slumped," has too coarse a sound to be used by a lady. [Eliza Leslie, "Miss Leslie's Behaviour Book," Philadelphia, 1839]Economic sense from 1888.
"act of slumping, slumping movement," 1850; "heavy decline in prices on the stock exchange," 1888, from slump (v.). Generalized by 1922 to "sharp decline in trade or business."
To descend to the level of the lower classes; to endure conditions or accommodations that are worse than what one is accustomed to: slumming it at the Holiday Inn