by 1953, name for human anti-coagulant use of the rat poison warfarin sodium, abstracted from the chemical name, 3-(α-acetonylbenzyl)-4-hydroxycoumarin; earlier known as Dicoumarol, it attained publicity when it was used in 1955 to treat U.S. President Dwight Eisenhower after a heart attack. Coumarin as the name of an aromatic crystalline substance is by 1830 in English, from French coumarine, from coumarou, the native name in Guyana of the tonka or tonquin bean, one source of the substance.

masc. proper name, also Charley, familiar form of Charles (also see -y (3)); 1965 in Vietnam War U.S. military slang for "Vietcong, Vietcong soldier," probably suggested by Victor Charlie, military communication code for V.C. (as abbreviation of Viet Cong), perhaps strengthened by World War II slang use of Charlie for Japanese soldiers, which itself is probably an extension of the 1930s derogatory application of Charlie to any Asian man, from fictional Chinese detective Charlie Chan.

Other applications include "a London night watchman" (1812); "a goatee beard" (1834, from portraits of King Charles I and his contemporaries); "a fox" (1857); in plural "a woman's breasts" (1874); "an infantryman's pack" (World War I); and "a white man" (Mr. Charlie), 1960, American English, from African-American vernacular.