for·bid·den (fər-bĭdn, fôr-)
A past participle of forbid.
1. Not allowed; not permitted: A sign at the entrance of the park lists forbidden substances, such as drugs and alcohol.
2. Physics Having a zero probability of occurrence. Used of quantum phenomena: a forbidden transition.
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2020 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.