The Collaborative International Dictionary of English v.0.48:

Sonorous \So*no"rous\, a. [L. sonorus, fr. sonor, -oris, a
   sound, akin to sonus a sound. See Sound.]
   1. Giving sound when struck; resonant; as, sonorous metals.
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   2. Loud-sounding; giving a clear or loud sound; as, a
      sonorous voice.
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   3. Yielding sound; characterized by sound; vocal; sonant; as,
      the vowels are sonorous.
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   4. Impressive in sound; high-sounding.
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            The Italian opera, amidst all the meanness and
            familiarty of the thoughts, has something beautiful
            and sonorous in the expression.       --Addison.
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            There is nothing of the artificial Johnsonian
            balance in his style. It is as often marked by a
            pregnant brevity as by a sonorous amplitude. --E.
                                                  Everett.
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   5. (Med.) Sonant; vibrant; hence, of sounds produced in a
      cavity, deep-toned; as, sonorous rhonchi.
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   Sonorous figures (Physics), figures formed by the
      vibrations of a substance capable of emitting a musical
      tone, as when the bow of a violin is drawn along the edge
      of a piece of glass or metal on which sand is strewed, and
      the sand arranges itself in figures according to the
      musical tone. Called also acoustic figures.

   Sonorous tumor (Med.), a tumor which emits a clear,
      resonant sound on percussion.
      [1913 Webster] -- So*no"rous*ly, adv. --
      So*no"rous*ness, n.
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WordNet (r) 3.0 (2006):

sonorousness
    n 1: having the character of a loud deep sound; the quality of
         being resonant [syn: plangency, resonance,
         reverberance, ringing, sonorousness, sonority,
         vibrancy]