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.
Known as Fish’s Number 7, or the titular Fish 7 for short, it is constructed by similarly unfathomable gargantuan ideas.
From The Wall Street Journal • May 29, 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
He doted on the music of Rachmaninoff when Rachmaninoff was unfashionable and on Steve Reich when Reich was found unfathomable.
From Los Angeles Times • Apr. 24, 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
This southron king seemed to be one of those men to whom women are another race, as strange and unfathomable as giants and grumkins and the children of the forest.
From "A Dance with Dragons" by George R. R. Martin
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.
