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.
The American Heritage Dictionary Blog
Check out our blog, updated regularly, for new words and revised definitions, interesting images from the 5th edition, discussions of usage, and more.