protreptic UK /pɹəʊˈtɹɛptɪk/US /pɹoʊˈtɹɛptɪk/adjective 1noun 1forms 3 adjective1 •Serving to instruct; didactic.A protreptic discourse for beginners, no matter what the stage of Plato's development when he wrote it, would contain much elementary matter and would certainly not reveal his most profound thought. — 1930 noun1 •A didactic speech, book, etc. formsprotreptics · more protreptic · most protreptic