by 1520s, "vendor of fancy wares, man who deals in articles for women's wear," probably originally Milaner "native or resident of Milan" (in Middle English Milain, Milein, Millein, etc.), the northern Italian city famous for straw works, fancy goods, silks, ribbons, bonnets, and cutlery. Milener as "a native or inhabitant of Milan" is attested in English from mid-15c. From 16c. to 18c. it is difficult to know whether the English word means a type of merchant or "a resident of Milan" who is selling certain wares. The original milliners were men; by 1713 the word was being used of "a woman who makes and sells bonnets and other headgear for women," and this was the prevailing sense of the word 19c.
noun suffix, in army, city, country, etc., from Old French -e, Latin -atus, -atum, past participle suffix of certain verbs, which in French came to be used to indicate "employment, office, dignity" (as in duché, clergié).