Source : Webster's Revised Unabridged Dictionary (1913)

Spontaneity \Spon`ta*ne"i*ty\, n.; pl. {Spontaneities}. [Cf. F.
   spontan['e]it['e].]
   1. The quality or state of being spontaneous, or acting from
      native feeling, proneness, or temperament, without
      constraint or external force.

            Romney Leigh, who lives by diagrams, And crosses not
            the spontaneities Of all his individual, personal
            life With formal universals.          --Mrs.
                                                  Browning.

   2. (Biol.)
      (a) The tendency to undergo change, characteristic of both
          animal and vegetable organisms, and not restrained or
          cheked by the environment.
      (b) The tendency to activity of muscular tissue, including
          the voluntary muscles, when in a state of healthful
          vigor and refreshment.

Source : WordNet®

spontaneity
     n : the quality of being spontaneous and coming from natural
         feelings without constraint; "the spontaneity of his
         laughter" [syn: {spontaneousness}]