1. Geology A thin, leaflike layer or stratum occurring especially in metamorphic rock.
2. Mathematics A plane cubic curve having a single loop, a node, and two ends asymptotic to the same line.
[Latin, leaf; see bhel-3 in the Appendix of Indo-European roots.]
(click for a larger image)folium
The equation of the folium of Descartes is x3 + y3 = 3axy.
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.