Probably borrowed from Old French Bonhomme. Bonhomme is a family name in France to this day and goes back to the Middle Ages (it turns up in England as Bonham as early as 1327); "bon nom", on the other hand, could be a calque of the Hebrew name שם טוב (shem tov), which reached southern France from Spain, as in the family of the 13th-century Provençal philosopher Shem-Tov ibn Falaquera. And if Bunim comes from "bon nom", it is actually a calque of a calque, since Shem Tov is a Hebraization of the Greek name Kalonymos, which appears in the Talmud, surfaces again in eighth-century Italy, belonging to a renowned Jewish family in the medieval Rhineland and eventually became the Eastern European Kalman.
בונים • (bunim) m