early 14c., "outline, plan, model, pattern;" early 15c. as "model of behavior, exemplar," from Old French patron and directly from Medieval Latin patronus (see patron).
Extended sense of "decorative design" first recorded 1580s, from earlier sense of a "patron" as a model to be imitated. The difference in form and sense between patron and pattern wasn't firm till 1700s. Meaning "model or design in dressmaking" (especially one of paper) is first recorded 1792, in Jane Austen.