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.
Bezos has an estimated net worth of around $250 billion, an unfathomable amount of money that makes him one of the richest people in the world.
From Los Angeles Times • May 5, 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
"If much younger people are being affected, why is the threshold so high for us to be diagnosed and diagnosed at an early stage? It just is unfathomable to me."
From BBC • Mar. 31, 2026
In the movie, Charli contends with the unfathomable triumph of “Brat” while fielding brand deal offers and label demands that reek of the capitalist desperation to extend the “Brat” era as long as possible.
From Salon • Feb. 8, 2026
His expression unfathomable, he returned to the party.
From "Harry Potter and the Half-Blood Prince" by J.K. Rowling
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.
