Green’s Dictionary of Slang

a sophisticated, smart person, both mentally and physically.

1925		O.O. McIntyre New York Day by Day 15 Sept. [synd. col.] The gate crasher is proud of his work [...] and is regarded as a smooth article.
1939		Howsley Argot: Dict. of Und. Sl. 46: smooth article —a nicely dressed, attractive female; a ‘slicker’.
1999		Indep. on Sun. Culture 15 Aug. 5: Lovable rogue, irresistable smoothie, gentlemanly cad.