"liquid food," 1650s, from French soupe "soup, broth" (13c.), from Late Latin suppa "bread soaked in broth," from a Germanic source (cf. Middle Dutch sop "sop, broth"), from Proto-Germanic *sup-, from PIE *sub-, from root *seue- (2) "to take liquid" (see sup (v.2)).
Primordial soup is from a concept first expressed 1929 by J.B.S. Haldane. Soup to nuts "everything" is from 1910. Soup-kitchen, "public establishment supported by voluntary contributions, for preparing and serving soup to the poor at no cost" is attested from 1839. In Ireland, souper meant "Protestant clergyman seeking to make proselytes by dispensing soup in charity" (1854).
"increase the horsepower of an engine," 1921, probably from soup (n.) in slang sense of "narcotic injected into horses to make them run faster" (1911), influenced by supercharge (v.).
Make something more powerful; especially, add speed to an engine. For example, He was riding around in that car he'd souped up, or They had to soup up the sound system for the outdoor concert. [Slang; c. 1930]