The Collaborative International Dictionary of English v.0.48:

Oratory \Or"a*to*ry\, n.; pl. Oratories. [OE. oratorie, fr. L.
   oratorium, fr. oratorius of praying, of an orator: cf. F.
   oratoire. See Orator, Oral, and cf. Oratorio.]
   A place of orisons, or prayer; especially, a chapel or small
   room set apart for private devotions.
   [1913 Webster]

         An oratory [temple] . . . in worship of Dian.
                                                  --Chaucer.
   [1913 Webster]

         Do not omit thy prayers for want of a good oratory, or
         place to pray in.                        --Jer. Taylor.
   [1913 Webster]

   Fathers of the Oratory (R. C. Ch.), a society of priests
      founded by St. Philip Neri, living in community, and not
      bound by a special vow. The members are called also
      oratorians.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Oratory \Or"a*to*ry\, n. [L. oratoria (sc. ars) the oratorical
   art.]
   The art of an orator; the art of public speaking in an
   eloquent or effective manner; the exercise of rhetorical
   skill in oral discourse; eloquence. "The oratory of Greece
   and Rome." --Milton.
   [1913 Webster]

         When a world of men
         Could not prevail with all their oratory. --Shak.
   [1913 Webster]

WordNet (r) 3.0 (2006):

oratory
    n 1: addressing an audience formally (usually a long and
         rhetorical address and often pompous); "he loved the sound
         of his own oratory"

Moby Thesaurus II by Grady Ward, 1.0:

57 Moby Thesaurus words for "oratory":
   Lady chapel, address, articulateness, articulation, chantry,
   chapel, chapel of ease, chapel royal, command of language,
   command of words, debating, declamation, demagogism, diction,
   effective style, elocution, eloquence, eloquent tongue,
   enunciation, expression, expressiveness, facundity, felicitousness,
   felicity, fluency, forensics, gift of expression, gift of gab,
   glibness, grandiloquence, graphicness, homiletics, lecturing,
   magniloquence, meaningfulness, oratorium, platform oratory,
   public speaking, pyrotechnics, rabble-rousing, rhetoric, sacellum,
   sacrament chapel, sacrarium, school chapel, side chapel,
   silver tongue, slickness, smoothness, speaking, speechcraft,
   speechification, speeching, speechmaking, stump speaking,
   vividness, wordcraft



The Devil's Dictionary (1881-1906):

ORATORY, n.  A conspiracy between speech and action to cheat the
understanding.  A tyranny tempered by stenography.