c. 1600, "capable of being fashioned," also "conforming to prevailing tastes," from fashion + -able. From 1620s as "stylish;" as a noun, "person of fashion," from 1800. Related: Fashionably "in a manner accordant with fashion, custom, or prevailing practice; with modish elegance;" fashionably late is by 1809.
She was somewhat surprised, especially as she came fashionably late, to find in the drawing-room only old Mrs. Wynne, her nephew, and a lady, who from her dress and modest appearance was evidently nobody. [Maria Edgworth, "Tales of Fashionable Life," 1809]