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."
early 15c., rethoricien, "writer on the art of rhetoric; professional orator; master of literary eloquence," from Old French rethoricien (Modern French rhétoricien), from rethorique (see rhetoric). An Old English word for one was wordsawere "word-sower."
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-15c., rethorical, "eloquent, according to the principles of rhetoric," from rhetoric (n.) or else from Latin rhetoricus (in Medieval Latin rethoricus), from Greek rhētorikos "oratorical, rhetorical; skilled in speaking," from rhētōr "orator."
The meaning "pertaining to rhetoric" is from 1520s. In later use also with implication of artificial extravagance. Rhetorical question, "statement put in the form of a question for rhetorical effect only and thus not requiring an answer," is from 1670s. Related: Rhetorically.
1590s, "a doubling," from Latin geminationem (nominative geminatio) "a doubling," noun of action from past-participle stem of geminare "to double, repeat" (see geminate). In rhetoric, repetition of a word or phrase for emphasis.
The extended sense of "direct or striking opposition" is from 1630s; as "that which is the direct opposite" from 1831.