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.]
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2019 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.