1. The apparent intersection of the earth and sky as seen by an observer. Also called apparent horizon.
a. See sensible horizon.
b. See celestial horizon.
c. The limit or edge of the observable universe.
3. The range of one's knowledge, experience, or interest.
a. A specific position in a column of rock layers, usually designated by the occurrence of one or more distinctive fossils or by a distinctive sediment bed, that is used in stratigraphy.
b. A layer of soil that can be distinguished from adjacent layers of soil and that is characterized by a certain color, texture, structure or chemical composition.
5. Archaeology A period during which the influence of a specified culture spread rapidly over a defined area: artifacts associated with the Olmec horizon in Mesoamerica.
[Middle English orizon, from Old French, from Latin horizōn, from Greek horizōn (kuklos), limiting (circle), horizon, present participle of horizein, to limit, from horos, boundary.]
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.