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

The Devil's Dictionary (1881-1906):

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