The Collaborative International Dictionary of English v.0.48:

Voluminous \Vo*lu"mi*nous\, a. [L. voluminosus: cf. F.
   volumineux.]
   Of or pertaining to volume or volumes. Specifically:
   [1913 Webster]
   (a) Consisting of many folds, coils, or convolutions.
       [1913 Webster]

             But ended foul in many a scaly fold,
             Voluminous and vast.                 --Milton.
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             Over which dusky draperies are hanging, and
             voluminous curtains have long since fallen. --De
                                                  Quincey.
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   (b) Of great volume, or bulk; large. --B. Jonson.
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   (c) Consisting of many volumes or books; as, the collections
       of Muratori are voluminous.
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   (d) Having written much, or produced many volumes; copious;
       diffuse; as, a voluminous writer.
       [1913 Webster] -- Vo*lu"mi*nous*ly, adv. --
       Vo*lu"mi*nous*ness, n.
       [1913 Webster]

WordNet (r) 3.0 (2006):

voluminousness
    n 1: greatness of volume [syn: fullness, voluminosity,
         voluminousness]