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.
“About a year ago, you guys did a truly unfathomable thing. Something that completely blew my mind…,” she wrote on Instagram.
From Los Angeles Times ● Sep. 23, 2026
But that’s the point of “Rock*.” It’s a lopsided hymn of praise to music—all music—that changes lives for very particular and ultimately unfathomable reasons.
From The Wall Street Journal ● Sep. 18, 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
“It’s unfathomable that we’re actually playing in this huge tournament,” Curaçao coach Dick Advocaat said.
From The Wall Street Journal ● Jun. 25, 2026
He could see it in their faces—in Joe’s contorted grimace, in Don Hume’s wide-open, astonished eyes, eyes that seemed to stare past him into some unfathomable void.
From "The Boys in the Boat: Nine Americans and Their Epic Quest for Gold at the 1936 Berlin Olympics" by Daniel James Brown
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.
