Collins Russian Dictionary 2nd Edition © HarperCollins Publishers 2000, 1997:
duplex [ˈdjuːplɛks] n (US) (also: duplex house) одна́ из часте́й двухкварти́рного до́ма; (also: duplex apartment) двухэта́жная кварти́ра
* is used to mark translations which have irregular inflections. The Russian-English side of the dictionary gives inflectional information.