1. The spinal column of a vertebrate.
2. Zoology Any of various pointed projections, processes, or appendages of animals.
a. A strong, sharp-pointed outgrowth derived from a leaf or leaf part.
b. Any of various similar sharp structures, such as a thorn.
4. Something that resembles or suggests a backbone, as:
a. The hinged back of a book.
b. The crest of a ridge.
5. Strength of character; courage or willpower.
[Middle English, from Old French espine, from Latin spīna.]
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.