unfathomable

adjective

un·​fath·​om·​able ˌən-ˈfa-t͟hə-mə-bəl How to pronounce unfathomable (audio)
Synonyms of unfathomable
: not capable of being fathomed:
a
: immeasurable
… the unfathomable darkness of empty space.—H. G. Wells
b
: impossible to comprehend
unfathomable motives/reasons
unfathomably
ˌən-ˈfa-t͟hə-mə-blē How to pronounce unfathomable (audio)
adverb

Synonyms of unfathomable

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Examples of unfathomable in a Sentence

His behavior is completely unfathomable. the unfathomable reaches of space
Recent Examples on the Web
Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.
Taken together, these two mistakes represented an almost-unfathomable breach of basic diligence. — Daniel Duane, New York Times, 14 Oct. 2026 The Baltimore Ravens were in a goal-to-go setting, trailing 23-15 and needing to do the statistically unfathomable — according to CBS, teams behind by 8-plus points inside the final minute had lost 581 straight games. — Daniel Flick, AJC.com, 12 Oct. 2026 From 2021 through last season, the Knicks boasted an unfathomable 18-2 record against their Eastern Conference counterpart Washington Wizards. — Kristian Winfield, New York Daily News, 9 Oct. 2026 The Street loves this stock for some unfathomable reason, even as the company is antithetical to its aims. — Jim Cramer, CNBC, 9 Oct. 2026 See All Example Sentences for unfathomable

Word History

First Known Use

1640, in the meaning defined above

Time Traveler
The first known use of unfathomable was in 1640

Browse Nearby Words

unfatherly
unfathomable
unfathomably
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Cite this Entry

“Unfathomable.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/unfathomable. Accessed 20 Oct. 2026.

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Kids Definition

unfathomable

adjective
un·​fath·​om·​able ˌən-ˈfat͟h-ə-mə-bəl How to pronounce unfathomable (audio)
: not capable of being fathomed:
a
: immeasurable
b
: impossible to understand
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