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Synonyms

fathom

American  
[fath-uhm] / ˈfæð əm /

noun

plural

fathoms,

plural

fathom

  1. a unit of length equal to six feet (1.8 meters): used chiefly in nautical measurements. fath

verb (used with object)

  1. to measure the depth of by means of a sounding line; sound.

  2. to penetrate to the truth of; comprehend; understand.

    to fathom someone's motives.
fathom British  
/ ˈfæðəm /

noun

  1. a unit of length equal to six feet (1.829 metres), used to measure depths of water

  2. mining a unit of volume usually equal to six cubic feet, used in measuring ore bodies

  3. forestry a unit of volume equal to six cubic feet, used for measuring timber

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

verb

  1. to measure the depth of, esp with a sounding line; sound

  2. to penetrate (a mystery, problem, etc); discover the meaning of

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Other Word Forms

  • fathomable adjective
  • fathomer noun
  • unfathomable adjective
  • unfathomed adjective

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” ( patent )

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.

"Can't even begin to fathom or process this," wrote Watt.

From Barron's • Feb. 22, 2026

“This was a special year, it’s hard to fathom that it’s over.”

From Los Angeles Times • Jan. 26, 2026

It is "hard to fathom just how quickly Heated Rivalry took the world by storm", Radio Times said last month.

From BBC • Jan. 7, 2026

To Ole Miss fans who have waited their entire lives for a postseason performance like that, Chambliss’s game was hard to fathom.

From The Wall Street Journal • Jan. 6, 2026

Lazlo couldn't fathom it, that a goddess would be willing to give up her magic.

From "Strange the Dreamer" by Laini Taylor

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.