1. Happening or arising without apparent external cause; self-generated: a microorganism capable of spontaneous movement.
2. Arising from a natural inclination or impulse and not from forethought or prompting: spontaneous laughter; a spontaneous protest.
3. Unconstrained and unstudied in manner or behavior: a spontaneous personality.
4. Growing without cultivation or human labor: spontaneous vegetation.
[From Late Latin spontāneus, of one's own accord, from Latin sponte; see (s)pen- in the Appendix of Indo-European roots.]
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