Automotive and aviation usage is attested at least since 1925 (in Popular Mechanics) — possibly from 1921 — with even early citations linking it to supercharged. Therefore, it is often contended that soup is a clipping of super.
However, this is antedated by usage in horse racing cant that applies the term to horses, and by a US Navy euphemism for drunkenness. The former is attested in Webster New International Dictionary (1909) and the latter in Our Navy (May 1915). Both may be figurative interpretations of soup as a liquid food item, although other origins cannot be discounted.
- (horse racing, cant) Of horses injected with something to make them run faster or change their temperament. [19th-early 20th c.]
- (US Navy, slang) Drunk.
- (of an engine, a motor vehicle or another device) Modified for higher performance.
2017 December 1, Tom Breihan, “Mad Max: Fury Road might already be the best action movie ever made”, in The Onion AV Club:
- He spent nearly 20 years developing the movie, keeping at it through false starts and heartbreaking dead ends. And when he got the chance to make it, he went all in, devising entire societies full of baroquely souped-up death machines and screaming war-cults.
- (Rhode Island, Massachusetts, Connecticut, slang) Excited.