Evidently, according to OED, ‘doozy’ made a quick trip, presumably via that early twentieth-century newfangled invention called the automobile, from an adjective to a noun. A wholly invented word, its contemporary cachet was enhanced both by the popularity of the actress Eleanora Duse, (the famous ‘la Duse’) and of the new Duesenberg, the luxury American car produced in the 20s and 30s – thus the allusion (above) to a car. For just a moment I thought it was la Duse who was killed in a tragic car accident in which her scarf tangled in the engine thus decapitating her, but this was, in fact, Isadora Duncan who was, in one of those serendipitous convolutions that propel my mind, a close friend of la Duse – but I digress.
However, other etymological sources reject this theory entirely, claiming a connection to a game called The Dozens, in which two individuals trade increasingly outrageous insults until one gives up – apparently a contest that originated in Africa and is still common in some African-American communities. This makes sense to me, as the original sense of a ‘doozy’ as something extraordinary or remarkable seems to have gravitated more towards the characterization of a exaggerated lie – although ‘whopper’ is more common – a word that also originated as a descriptor for something large or remarkable.
doozy also doozie, 1903 (adj.), 1916 (n.), perhaps an alteration of daisy, or from popular Italian actress Eleonora Duse (1859-1924). In either case, reinforced by Duesenberg, the expensive, classy make of automobile from the 1920s-30s.