a place of prayer, as a small chapel or a room for private devotions.
2.
(initial capital letter) Roman Catholic Church. any of the religious societies of secular priests who live in religious communities but do not take vows.
Origin: 1300–50; Middle English < Late Latin ōrātōrium place of prayer. See orator, -tory2
"formal public speaking, the art of eloquence," 1586, from L. (ars) oratoria "oratorical (art)," fem. of oratorius "of speaking or pleading," from orare (see orator).
"small chapel," c.1300, from L.L. oratorium "place of prayer" (especially the Oratory of St. Philip Neri in Rome, where musical services were presented), properly an adj., as in oratorium templum, from neut. of L. oratorius "of or for praying," from orare (see orator).