Pronunciation: (spon-tā'nē-us),[key] —adj. 1. coming or resulting from a natural impulse or tendency; without effort or premeditation; natural and unconstrained; unplanned: a spontaneous burst of applause. 2. (of a person) given to acting upon sudden impulses.
3. (of natural phenomena) arising from internal forces or causes; independent of external agencies; self-acting.
4. growing naturally or without cultivation, as plants and fruits; indigenous.
5. produced by natural process.