late 14c., rethor, "master or teacher of rhetoric," also "an ancient Greek orator," from Old French retor (Modern French rhéteur), from Latin rhetor (in Medieval Latin also rethor), from Greek rhētōr "speaker, master speaker, orator; artist of discourse; teacher of rhetoric" (see rhetoric (n.)).
mid-14c., prompten, "to incite to action, urge," from the adjective or from Latin promptus, past participle of promere "to bring forth," from pro "forward" (from PIE root *per- (1) "forward") + emere "to take" (from PIE root *em- "to take, distribute").
The meaning "coach (someone), assist (a learner or speaker) by suggesting something forgotten or imperfectly learned or known" is from early 15c.; specifically in the theatrical sense of "to assist a speaker with lines" by 1670s. Related: Prompted; prompting.
1824, "male performer or speaker making his first public appearance," from French debutant, noun use of present participle of débuter "to make the first strike" (in billiards, etc.), from debut (see debut).