The Collaborative International Dictionary of English v.0.48:

Numerous \Nu"mer*ous\, a. [L. numerosus. See Number.]
   1. Consisting of a great number of units or individual
      objects; being many; as, a numerous army; numerous
      objections.
      [1913 Webster]

            Such and so numerous was their chivalry. --Milton.
      [1913 Webster]

   2. Consisting of poetic numbers; rhythmical; measured and
      counted; melodious; musical. [Obs.]
      [1913 Webster]

            Such prompt eloquence
            Flowed from their lips, in prose or numerous verse.
                                                  --Milton.
      [1913 Webster] -- Nu"mer*ous*ly, adv. --
      Nu"mer*ous*ness, n.
      [1913 Webster]

WordNet (r) 3.0 (2006):

numerousness
    n 1: a large number [syn: numerousness, numerosity,
         multiplicity]