1. Incapable of being expressed; indescribable or unutterable: ineffable joy.
2. Not to be uttered; taboo: the ineffable name of God.
[Middle English, from Old French, from Latin ineffābilis : in-, not; see IN-1 + effābilis, utterable (from effārī, to utter : ex-, ex- + fārī, to speak; see bhā-2 in the Appendix of Indo-European roots).]
in·ef′fa·bili·ty, in·effa·ble·ness n.
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 Appendicies
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.