fathom
Americannoun
plural
fathoms,plural
fathomverb (used with object)
-
to measure the depth of by means of a sounding line; sound.
-
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
-
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
-
to measure the depth of, esp with a sounding line; sound
-
to penetrate (a mystery, problem, etc); discover the meaning of
Other Word Forms
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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The Old Man and the Sea
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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.
Protagonist Louden Swain, a high-school senior, can’t fathom why Elmo, an older and impecunious cook at the hotel where they’re both employed, is missing work to watch him wrestle.
From The Wall Street Journal • May 13, 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
"When you have players who play really well one week and the following two weeks don't, it's hard to fathom."
From BBC • Apr. 3, 2026
"Can't even begin to fathom or process this," wrote Watt.
From Barron's • Feb. 22, 2026
Kamen could not fathom how Lawrence expected to be immune from courtroom questioning; he supposed, undoubtedly correctly, that Ernest was “not prepared to undergo the trauma of an adversary confrontation.”
From "Big Science" by Michael Hiltzik
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.
