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

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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

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verb

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

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

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” ( 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."

Example Sentences

Mr. Boone initially creates only a mild impression, making Seth’s suspicion of him and discomfort in his presence hard to fathom.

From The Wall Street Journal • Apr. 26, 2026

She said it’s important for providers to remember that many residents “have experienced trauma most people could not fathom going through.”

From Los Angeles Times • Apr. 14, 2026

It’s a situation that is almost impossible to fathom, considering the U.S. entered the WBC boasting several billion dollars’ worth of talent.

From The Wall Street Journal • Mar. 12, 2026

"I can't fully fathom what's going on!" he said.

From Barron's • Feb. 11, 2026

If we cannot literally talk to a work of art, we can learn how to respond to it and question it in order to fathom its meaning.

From "History of Art, Volume 1" by H.W. Janson

Related Words

• appreciate
• comprehend
• divine
• figure out
• grasp
• penetrate
• pinpoint
• plumb
• unravel