Spontaneous /(spŏn*tā"nē̇*ŭs)/

Spon·ta·ne·ous

Spontaneous

a.
  1. Proceeding from natural feeling, temperament, or disposition, or from a native internal proneness, readiness, or tendency, without constraint; as, a spontaneous gift or proposition.
  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 joys, where nature has its play, The soul adopts, and owns their firstborn away.

Phrases & Compounds
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
See under Generation.