\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.