\Spon*ta"ne*ous\, a. [L. spontaneus, fr. sponte of
free will, voluntarily.]
1. Proceding from natural feeling, temperament, or
   disposition, or from a native internal proneness,
   readiness, or tendency, without constraint; as, a
   spontaneous gift or proportion.
2. Proceeding from, or acting by, internal impulse, energy,
   or natural law, without external force; as, spontaneous
   motion; spontaneous growth.
3. Produced without being planted, or without human labor;
   as, a spontaneous growth of wood.
{Spontaneous combustion}, combustion produced in a substance
   by the evolution of heat through the chemical action of
   its own elements; as, the spontaneous combustion of waste
   matter saturated with oil.
{Spontaneous generation}. (Biol.) See under {Generation}.
Syn: Voluntary; uncompelled; willing.
Usage: {Spontaneous}, {Voluntary}. What is voluntary is the
       result of a volition, or act of choice; it therefore
       implies some degree of consideration, and may be the
       result of mere reason without excited feeling. What is
       spontaneous springs wholly from feeling, or a sudden
       impulse which admits of no reflection; as, a
       spontaneous burst of applause. Hence, the term is also
       applied to things inanimate when they are produced
       without the determinate purpose or care of man.
       ``Abstinence which is but voluntary fasting, and . . .
       exercise which is but voluntary labor.'' --J. Seed.
             Spontaneous joys, where nature has its play, The
             soul adopts, and owns their firstborn away.
                                               --Goldsmith.
       -- {Spon*ta"ne*ous*ly}, adv. -- {Spon*ta"ne*ous*ness},
       n.