dip·lo·e or dip·lo·ë (dĭplō-ē′)
The spongy, porous, bony tissue between the hard outer and inner bone layers of the cranium.
[Greek diploē, a fold, doubling, from feminine of diploos, twofold; see dwo- in the Appendix of Indo-European roots.]
diplo·ic (-lō-ĭk) adj.
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 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.