c.1300, "shape, manner, mode," from Old French façon (12c.) "face, appearance; construction, pattern, design; thing done; beauty; manner, characteristic feature," from Latin factionem (nominative factio) "group of people acting together," literally "a making or doing," from facere "to make" (see factitious).
Sense of "prevailing custom" is from late 15c.; that of "style of attire" is from 1520s.
Fashion plate (1851) originally was "full-page picture in a popular magazine showing the prevailing or latest style of dress," in reference to the typographic "plate" from which it was printed. Transfered sense of "well-dressed person" had emerged by 1920s.