Source : Webster's Revised Unabridged Dictionary (1913)

Multitudinous \Mul`ti*tu"di*nous\, a.
   1. Consisting of a multitude; manifold in number or
      condition; as, multitudinous waves. ``The multitudinous
      seas.'' --Shak.

            A renewed jingling of multitudinous chains. --G.
                                                  Kennan.

   2. Of or pertaining to a multitude. ``The multitudinous
      tongue.'' --Shak. -- {Mul`ti*tu"di*nous*ly}, adv. --
      {Mul`ti*tu"di*nous*ness}, n.

Source : WordNet®

multitudinousness
     n : a very large number (especially of people)