Source : Webster's Revised Unabridged Dictionary (1913)

Sound \Sound\, n. [OE. soun, OF. son, sun, F. son, fr. L. sonus
   akin to Skr. svana sound, svan to sound, and perh. to E.
   swan. Cf. {Assonant}, {Consonant}, {Person}, {Sonata},
   {Sonnet}, {Sonorous}, {Swan}.]
   1. The peceived object occasioned by the impulse or vibration
      of a material substance affecting the ear; a sensation or
      perception of the mind received through the ear, and
      produced by the impulse or vibration of the air or other
      medium with which the ear is in contact; the effect of an
      impression made on the organs of hearing by an impulse or
      vibration of the air caused by a collision of bodies, or
      by other means; noise; report; as, the sound of a drum;
      the sound of the human voice; a horrid sound; a charming
      sound; a sharp, high, or shrill sound.

            The warlike sound Of trumpets loud and clarions.
                                                  --Milton.

   2. The occasion of sound; the impulse or vibration which
      would occasion sound to a percipient if present with
      unimpaired; hence, the theory of vibrations in elastic
      media such cause sound; as, a treatise on sound.

   Note: In this sense, sounds are spoken of as audible and
         inaudible.

   3. Noise without signification; empty noise; noise and
      nothing else.

            Sense and not sound . . . must be the principle.
                                                  --Locke.

   {Sound boarding}, boards for holding pugging, placed in
      partitions of under floors in order to deaden sounds.

   {Sound bow}, in a series of transverse sections of a bell,
      that segment against which the clapper strikes, being the
      part which is most efficacious in producing the sound. See
      Illust. of {Bell}.

   {Sound post}. (Mus.) See {Sounding post}, under {Sounding}.

Source : WordNet®

sound bow
     n : contact (the part of a bell) against which the clapper
         strikes