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.
“It is unfathomable they have had to wait this long to learn what happened to their daughter.”
From Los Angeles Times • Apr. 22, 2026
"It is unfathomable they have had to wait this long to learn what happened to their daughter," said Ukpo, who had criticised the decision to hold off on releasing their findings.
From BBC • Apr. 22, 2026
Even more unfathomable today is that cars were just sitting there at dealerships, waiting to be sold.
From The Wall Street Journal • Apr. 10, 2026
Buying a $1 million building — even if you’re sharing it with tenants — may simply feel unfathomable to them.
From MarketWatch • Apr. 3, 2026
She was proud of how calm she’d managed to make herself, standing there without even a tremble, waiting for some unfathomable wraith to come and deal with her.
From "Shadowshaper" by Daniel José Older
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.
