slump (v.)

1670s, "fall or sink 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]

Economic sense from 1888.

slump (n.)

"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."

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Definitions of slump from WordNet
slump (v.)
assume a drooping posture or carriage;
Synonyms: slouch
slump (v.)
fall or sink heavily;
He slumped onto the couch
Synonyms: slide down / sink
slump (v.)
fall heavily or suddenly; decline markedly;
Synonyms: fall off / sink
slump (v.)
go down in value;
prices slumped
Synonyms: decline / correct
slump (n.)
a noticeable deterioration in performance or quality;
the team went into a slump
Synonyms: slack / drop-off / falloff / falling off
slump (n.)
a long-term economic state characterized by unemployment and low prices and low levels of trade and investment;
Synonyms: depression / economic crisis