Person who produces flour or other products by operating a mill
A miller is a person who operates a mill, a machine to grind a grain (for example corn or wheat) to make flour. Milling is among the oldest of human occupations. "Miller", "Milne" and other variants are common surnames, as are their equivalents in other languages around the world ("Melnyk" in Ukrainian, "Meunier" in French, "Müller" or "Mueller" in German, "Mulder" and "Molenaar" in Dutch, "Molnár" in Hungarian, "Molinero" in Spanish, "Molinaro" or "Molinari" in Italian, "Mlinar" in South Slavic languages etc.).
https://en.wikipedia.org/wiki/Miller