1. A material formation or structure, such as a mountain range or wall, that prevents passage or access.
2. Something immaterial that obstructs or impedes: Lack of education can be a barrier to success.
3. Physiology A membrane, tissue, or mechanism that blocks the passage of certain substances.
4. Ecology A physical or biological factor that limits the migration, interbreeding, or free movement of individuals or populations.
5. A movable gate that keeps racehorses in line before the start of a race.
6. often barriers The palisades or fences enclosing the lists of a medieval tournament.
7. Geology An ice barrier.
[Middle English barrer, from Old French barriere, from Vulgar Latin *barrāria, from *barra, bar.]
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.