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.
But with a quarter-century of hindsight, asking the mayor to remove himself from a solemn commemoration of the greatest tragedy to ever occur in his city is unfathomable.
From Salon ● Sep. 11, 2026
Despite the failings in Jaafri's care, "and for reasons which remain unfathomable", the death was not reported to him by doctors at the hospital, nor the medical examiner, the coroner said.
From BBC ● Aug. 18, 2026
At this time, we ask for the privacy to grieve this unfathomable loss.
From Los Angeles Times ● Aug. 15, 2026
A year ago, the idea of intentionally walking the batter ahead of Cal Raleigh would’ve been completely unfathomable.
From The Wall Street Journal ● Aug. 7, 2026
He tried to return the gaze, looking into Goddard’s own cold place, but he found it opaque and unfathomable.
From "Scythe" by Neal Shusterman
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.
