Deusy would apply to the car. But it seems that might not be the orgination of this slang.
1) Doozy could be an alteration of an older slang, "It's a daisy," meaning something beautiful. 2) It could have originated around a popular Italian actress during the late 1800s, early 1900s, Eleonora Duse, who often simply went as Duse. 3) According to this video over on Webster, doozy originally appeared as "dozy" in eastern Ohio in 1916 -- four years prior to the production of the first Duesenberg vehicles. They also claim there is little evidence connecting the Duesenberg and doozy during the '20s and '30s, when the car was most popular. "Dozy" is akin to the verb "dozen" that is semantically and etymologically related to "daze." 4) Finally, many people DO, indeed, attribute it the majesty of the Duesenberg car after all, which after doing my research, does seem the most interesting at least, despite what Webster says.
2001 Lincoln Cont 4.6L DOHC/ 39K mi / QS HM 5w30 / FUG XG2 1999 Camaro SS M6 /19K /Mobil 1 0w40 /Fram UG /GM MTL-ATF 1969 Ply GTX/RRs