1540s, "one who or that which incites to action," agent noun from prompt (v.)). Earlier was promptator (mid-15c.), from Medieval Latin. Meaning "one who helps a speaker or reciter" is from 1590s; the specific theatrical sense is from c. 1600.
early 14c., rethorike, "the art of eloquence and persuasiveness in language, the art of using language to influence others," from Old French retorike, rethorique (Modern French rhétorique) and directly from Latin rhetorice, from Greek rhētorikētekhnē "art of an orator," from rhētōr (genitive rhētoros) "speaker, master speaker, orator; artist of discourse; teacher of rhetoric," especially (in the Attic official language), "orator in public." This is related to rhesis "speech," rhema "word, phrase, verb," literally "that which is spoken" (from PIE *wre-tor-, from root *were- (3) "to speak;" see verb). Since classical times with a derogatory suggestion of "artificial oratory" as opposed to what is natural or unaffected, "ostentatious declamation."
late 14c., oratour, "an eloquent or skilled speaker; one who pleads or argues for a cause," from Anglo-French oratour (Modern French orateur) and directly from Latin orator "speaker," from ōrare "to speak, speak before a court or assembly, pray to, plead."
This is sometimes said to be from PIE root *or- "to pronounce a ritual formula" (source also of Sanskrit aryanti "they praise," Homeric Greek are, Attic ara "prayer," Hittite ariya- "to ask the oracle," aruwai- "to revere, worship"). But according to de Vaan, the Latin word is rather from Proto-Italic *ōs- "mouth," from PIE *os- "mouth" (see oral). He writes:
The chronology of the attestations shows that 'to plead, speak openly' is the original meaning of orare .... The alternative etymology ... seems very unlikely to me: a connection with Skt. a-aryanti 'they acknowledge' and Ru. orat' 'to shout', since nothing suggests a meaning 'to shout' for the Latin verb, nor does it seem onomatopoeic.
The general meaning "public speaker," is attested from early 15c. Fem. forms were oratrice (early 15c., from Anglo-French); oratrix (mid-15c., from Latin); oratress (1580s).
"without doubt, without objection or uncertainty," late 14c., from doubt (n.) + -less. From late 14c. as an adjective, "beyond dispute, certain;" from mid-15c. as "free from doubt." Later in a weakened sense, indicating merely something that to the speaker seems likely to be true. Related: Doubtlessly.
"make mention of, speak of briefly or cursorily," 1520s, from mention (n.) or else from French mentionner, from Old French mencion. Related: Mentioned; mentioning. Not to mention as a "rhetorical suggestion that the speaker is refraining from presenting the full strength of his case" [OED] is by 1690s. Don't mention it as a conventional reply to expressions of gratitude or apology is attested from 1840.
1590s, from French ultramontain "beyond the mountains" (especially the Alps), from Old French (early 14c.), from Latin ultra "beyond" (from suffixed form of PIE root *al- (1) "beyond") + stem of mons "hill" (from PIE root *men- (2) "to project"). Used especially of papal authority, though "connotation varies according to the position of the speaker or writer." [Weekley]