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.
“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
The next challenge is maintaining the level she has shown at Queen's - arguably her best tennis since that unfathomable US Open triumph - for a sustained stretch of time.
From BBC ● Jun. 14, 2026
Japan is facing inflation for the first time in decades, with core inflation rising 2% to 3%, unfathomable a decade ago in the depths of Japan’s deflationary rout.
From Barron's ● May 20, 2026
The money sloshing around AI today was unfathomable not long ago.
From The Wall Street Journal ● May 18, 2026
The presumed deception, including within their own family, is so deep as to be unfathomable.
From "American Spirits" by Barb Rosenstock
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.
