Etymology
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guinea pig (n.)
rodent native to South America, 1660s. It does not come from Guinea and has nothing to do with the pig. Perhaps so called either because it was brought back to Britain aboard Guinea-men, ships that plied the triangle trade between England, Guinea, and South America [Barnhart, Klein], or from its resemblance to the young of the Guinea-hog "river pig" [OED], or from confusion of Guinea with the South American region of Guyana (but OED is against this). Pig probably for its grunting noises. In the extended sense of "one subjected to an experiment" it is first recorded 1920, because they were commonly used in medical experiments (by 1865).
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gun moll (n.)
"female criminal," 1908, second element from nickname of Mary, used of disreputable females since early 1600s; first element from slang gonif "thief" (1885), from Yiddish, from Hebrew gannabh "thief" (compare gonoph); influenced by gun (n.).
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gung ho (adj.)

also gung-ho, gungho, 1942, slang motto of Carlson's Raiders (2nd Marine Raider Battalion, under Lt. Col. Evans Carlson, 1896-1947), U.S. guerrilla unit operating in the Pacific in World War II, from Chinese kung ho "work together, cooperate." Widely adopted in American English 1959.

Borrowing an idea from China, Carlson frequently has what he calls 'kung-hou' meetings .... Problems are threshed out and orders explained. [New York Times Magazine, Nov. 8, 1942]
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