adjective
-
incapable of being fathomed; immeasurable
-
incomprehensible
Other Word Forms
Etymology
Origin of unfathomable
First recorded in 1610–20; un- 1 ( def. ) + fathom ( def. ) + -able ( def. )
Explanation
Unfathomable means impossible to ever understand. For most people, the field of quantum mechanics is unfathomable. Fathoms are seafaring units of measure equaling about six feet. So something that is unfathomable is also immeasurable, especially when it comes to depth. If your sonar isn't bouncing anything back to you, you're dealing with an unfathomable distance. Metaphorically, unfathomable can refer to something that resembles an abyss, some figurative notion that's so deep you can't even measure it.
Vocabulary lists containing unfathomable
The Outsiders
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"To Kill a Mockingbird" by Harper Lee, Chapters 7–11
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"The Black Cat" by Edgar Allan Poe
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Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
Despite the failings in Jaafri's care, "and for reasons which remain unfathomable", the death was not reported to him by doctors at the hospital, nor the medical examiner, the coroner said.
From BBC ● Aug. 18, 2026
At this time, we ask for the privacy to grieve this unfathomable loss.
From Los Angeles Times ● Aug. 15, 2026
Yet the salary cap also explains why teams are increasingly willing to give out deals that were previously unfathomable.
From The Wall Street Journal ● Aug. 10, 2026
“The idea that we’re competing with the market would have been unfathomable a few years ago,” said Margaret Salazar, CEO of Reach Community Development Corporation, one of Portland’s largest affordable housing providers.
From Salon ● Jul. 4, 2026
He discovered a scheme of energies—the same unfathomable force that kept the citadel in the sky—and he could feel it all.
From "Strange the Dreamer" by Laini Taylor
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
