fathom
Americannoun
verb (used with object)
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to measure the depth of by means of a sounding line; sound.
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to penetrate to the truth of; comprehend; understand.
to fathom someone's motives.
noun
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a unit of length equal to six feet (1.829 metres), used to measure depths of water
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mining a unit of volume usually equal to six cubic feet, used in measuring ore bodies
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forestry a unit of volume equal to six cubic feet, used for measuring timber
verb
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to measure the depth of, esp with a sounding line; sound
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to penetrate (a mystery, problem, etc); discover the meaning of
Other Word Forms
Derived Forms
Inflected Forms
Nouns
Participles
Conjugated Forms
Present
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fathomsimple
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fathomssimple
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have fathomedperfect
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has fathomedperfect
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am fathomingprogressive
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are fathomingprogressive
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is fathomingprogressive
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have been fathomingperfect progressive
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has been fathomingperfect progressive
Past
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fathomedsimple
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had fathomedperfect
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was fathomingprogressive
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were fathomingprogressive
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had been fathomingperfect progressive
Future
Etymology
Origin of fathom
First recorded before 900; Middle English fathme, Old English fæthm “span of outstretched arms”; cognate with German Faden “six-foot measure,” Old Norse fathmr; akin to Latin patēre “to stand open” ( see patent)
Explanation
To fathom something is to understand it thoroughly. It's usually used in the negative, as in "I can't fathom why he doesn't want to go along with us." Fathom is from Middle English fadme, from Old English fæthm, "outstretched arms." The Old English and modern English noun also refers to a unit of length used to measure the depth of water. The sense of intellectual depth comes from that meaning — to understand or fathom something thoroughly is "to get to the bottom of it."
Vocabulary lists containing fathom
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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.
See Examples For:
Rival athletic directors and coaches couldn’t fathom how someone who had so blatantly broken a universal rule would be allowed to escape with a slap on the wrist.
From The Wall Street Journal ● Jun. 23, 2026
The septet's mammoth global tour was making a stop in her backyard – the Indonesian capital, Jakarta – and as a longtime fan, she couldn't fathom missing it.
From BBC ● Jun. 21, 2026
UK-based Destiny content creator My name is Byf posted: "Saying goodbye like this is more painful than I can fathom," adding: "I can only hope the road doesn't end here for good."
From BBC ● May 22, 2026
But even they came around faster than the burgeoning class of prestige TV era viewers who couldn’t fathom that the new “Battlestar” could be as culturally resonant as, say, “The Sopranos” or “The Wire.”
From Salon ● May 5, 2026
For reasons that he couldn’t quite fathom, he didn’t mind terribly when Juliet called him by the pet name his mother had for him.
From "Artemis Fowl" by Eoin Colfer
DaCosta fathoms the deepest notes in Ibsen’s classic as though they were whale song, remixing them into her own ode to a woman who needs healthier hobbies.
From Los Angeles Times ● Mar. 10, 2026
In the late 1800s the Yup’ik people from the Alaskan coast recorded building kayaks that were 2.5 fathoms long plus a cockpit, which was the length of an arm with a closed fist.
From Science Magazine ● May 31, 2023
“He’s playing it off. I don’t think he fathoms how bad this is. Shame on him. I hope he gets what he deserves.”
From Washington Times ● Jul. 6, 2021
And after some initial tests in the shallow water, the Thresher headed out to where the ocean was 1,400 fathoms, or a mile and half, deep.
From Washington Post ● Sep. 26, 2019
He looked wildly up at the frowning wall, where the road-builders of old had cut the rock sheer for many fathoms above their heads.
From "The Return of the King" by J.R.R. Tolkien
Ken Ono’s career as one of the world’s most prominent mathematicians has taken him to Hollywood and the Olympics, places that he never could have fathomed.
From The Wall Street Journal ● Dec. 7, 2025
"We never fathomed it would be this catastrophic and apocalyptic."
From BBC ● Jan. 14, 2025
“He did something she could have never anticipated or fathomed or predicted,” Ms. Smith said.
From New York Times ● Jan. 25, 2024
Jeni and Christina, who didn’t want their last names used for privacy reasons, made the decision that neither ever fathomed they would make: ending a wanted pregnancy in the third trimester.
From Los Angeles Times ● Aug. 5, 2022
But I never fathomed the need of the culture even for the smallest acts.
From "Native Speaker" by Chang-rae Lee
While James is a good-looking, good-natured young man, he's rather lost when it comes to fathoming the way Pünd can unravel mysteries.
From Salon ● Oct. 31, 2022
But fathoming other universes is the essence of Theo’s job.
From Washington Post ● Sep. 21, 2021
Now, though some of the references have become more obscure with time, it’s hard to imagine anyone not fathoming the play’s gist.
From New York Times ● May 7, 2021
They are like the proverbial worker who knows how to use a hammer and thus sees everything as a nail—not fathoming the existence of other tools.
From Scientific American ● Jun. 8, 2020
I will pray your good angel to show me some means of fathoming the trouble in your soul.
From A Twofold Life by Hillern, Wilhelmine von
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.