The ambiguous phrase magnus rabinus likely meant great teacher, not a convert from Judaism

Evidence

Chronicler Pere Marsili asserts that Martí was a “Magnus Rabinus in Hebraeo,” which some have taken to mean that he was a convert from Judaism and perhaps a former rabbi, though Jeremy Cohen (The Friars and the Jews: The Evolution of Medieval Anti-Judaism [Ithaca: Cornell University Press, 1982], 130n) argues convincingly that this is unlikely, and that “magnus Rabinus” means simply “a great teacher of Hebrew.” — John V. Tolan, Saracens, 1914

Categorization

• DEFINE: Clarifies the meaning of the medieval Latin phrase “magnus rabinus” against a common misreading.