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).
c. 1600, "to pray, to plead," from Latin oratus, past participle of ōrare "speak, pray to, plead, speak before a court or assembly" (see orator). The meaning "make a formal speech, talk loftily," used humorously or contemptuously, emerged c. 1860 in American English as a back-formation of oration. Related: Orated; orating.
late 14c., oracioun, "a prayer," from Late Latin orationem (nominative oratio) "a speaking, speech, discourse; language, faculty of speech, mode of expressing; prayer," noun of action from past-participle stem of Latin ōrare "to pray to, plead, speak before an assembly" (see orator). The usual Old French form was oraison. Meaning "formal speech, discourse, eloquent or weighty address" is recorded from c. 1500.
"small chapel for prayer or worship," early 14c., oratorie, from Old French oratorie and directly from Late Latin oratorium "place of prayer" (especially the Oratory of St. Philip Neri in Rome, where musical services were presented; see oratorio), noun use of an adjective, as in oratorium templum, from neuter of Latin oratorius "of or for praying," from ōrare "to pray, plead, speak" (see orator).
"formal public speaking; the art of eloquence," 1580s, from Latin (ars) oratoria "oratorical (art)," fem. of oratorius "of speaking or pleading, pertaining to an orator," from ōrare "to speak, pray, plead" (see orator).
Oratory is the art or the act of speaking, or the speech. Rhetoric is the theory of the art of composing discourse in either the spoken or the written form. Elocution is the manner of speaking or the theory of the art of speaking ...: the word is equally applicable to the presentation of one's own or of another's thoughts. [Century Dictionary]
"unyielding, unrelenting," 1550s, from French inexorable and directly from Latin inexorabilis "that cannot be moved by entreaty, unyielding," from in- "not, opposite of" (see in- (1)) + exorabilis "able to be entreated," from exorare "to prevail upon," from ex "out" (see ex-) + ōrare "to pray to, beseech" (see orator). Related: Inexorably; inexorability.
c. 1200, orisoun, "a prayer," especially "a set prayer that forms part of a religious service," from Anglo-French oreison, Old French oreisun (12c., Modern French oraison) "oration," from Latin orationem (nominative oratio) "speech, oration," in Church Latin "prayer, appeal to God," noun of action from past-participle stem of ōrare "to speak, pray, plead" (see orator). Etymologically, a doublet of oration.
mid-15c., peroracioun, "a speech, an address," in rhetoric, "the concluding part of an address," involving an emphatic restatement of the principal points, from Latin perorationem (nominative peroratio) "the ending of a speech or argument of a case," from past-participle stem of perorare "argue a case to the end, bring a speech to a close," from per "to the end," hence "thoroughly, completely" (from PIE root *per- (1) "forward," hence "through") + ōrare "to speak, plead" (see orator).
"long musical composition, usually with a text based on Scripture," 1727 (in English from 1640s in native form oratory), from Italian oratorio (late 16c.), from Church Latin oratorium "a place of prayer, an oratory or chapel," noun use of an adjective, as in oratorium templum, from neuter of Latin oratorius "of or for praying," from ōrare "to pray, plead, speak" (see orator). The purely musical sense stems from the Oratory musical services of prayers and hymns instituted in Rome in the 1550s by St. Philip Neri and performed in the church of Santa Maria in Vallicella.