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doozy (plural doozies)
- (US) something that is extraordinary. Often used in the context of troublesome, difficult or problematic, but can be used positively as well.
- Most of the test was easy, but the last question was a doozy.
- (slang, dated) Of high quality; remarkable; excellent. 
1903, Alfred Leon Kleberg, Slang Fables from Afar, page 83:
- As soon as the races were billed he began to evolve Schemes — one Doozy scheme followed the other...
2011, “Feeling Pinkie Keen”, in My Little Pony: Friendship is Magic:
- The hydra wasn't the doozy? How could it not be the doozy? What could be doozier than that?
- (slang, US, archaic) Sporty, ostentatious, flashy. 
1917, Elsie Warnock, “Terms of approbation and eulogy in American dialect speech”, in Dialect Notes, volume IV, page 21:
- Who was that doozy fellow I saw you with?
1920, Jane Barrett, “English review”, in High School Life, volume 21, page 531:
- Sweetie, do let me show you the dooziest little afternoon frock that Poiret designed for me in Paris.
- "Doozy" in Michael Quinion, Ballyhoo, Buckaroo, and Spuds, 2004.
- "Doozy" in J.E. Lighter, Random House Historical Dictionary of American Slang volume 1, 1994.