slump v.

1670s, "fall or sink suddenly into a muddy place," probably from a Scandinavian source such as 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]

Used figuratively of failure or falling through; the economic sense is by 1888.

1850, "act of slumping, slumping movement;" 1888 as "heavy decline in prices on the stock exchange," from slump (v.). Generalized by 1896 to "sharp decline in trade or business."