The Collaborative International Dictionary of English v.0.48:

Multiplicity \Mul`ti*plic"ity\, n. [Cf. F. multiplicit['e].]
   The quality of being multiple, manifold, or various; a state
   of being many; a multitude; as, a multiplicity of thoughts or
   objects. "A multiplicity of goods." --South.
   [1913 Webster]

WordNet (r) 3.0 (2006):

multiplicity
    n 1: the property of being multiple
    2: a large number [syn: numerousness, numerosity,
       multiplicity]