fathom

verb

fathomed; fathoming; fathoms

intransitive verb

1

: probe

2

: to take soundings

transitive verb

1

: to measure by a sounding line

2

: to penetrate and come to understand

couldn't fathom the problem

fathomable

ˈfa-t͟hə-mə-bəl 

adjective

Did you know?

Did fathom Always Refer to a Measurement?

Fathom comes from the Old English word fæthm, meaning "outstretched arms." The noun fathom, which now commonly refers to a measure (especially of depth) of six feet, was originally used for the distance, fingertip to fingertip, created by stretching one's arms straight out from the sides of the body. In one of its earliest uses, the verb fathom was a synonym of our modern embrace: to fathom someone was to encircle the person with your arms. By the 1600s fathom had taken to the seas, with the verb being used to mean "to measure by a sounding line." At the same time, the verb also developed senses synonymous with probe and investigate, and it is now frequently used to refer to the act of getting to the bottom of something, figuratively speaking.

Synonyms of fathom

• plumb
• scale
• span

Examples of fathom in a Sentence

the pilot had to continually fathom the river, which drought conditions had lowered to unprecedented levels

Recent Examples on the Web

Of all the reasons why the Colorado Avalanche are no longer participating in this tournament, that is the hardest one to fathom. —Corey Masisak, Denver Post, 27 May 2026

The decision of the soap press to even cover the show proved contentious for the genre’s devotees, who just couldn’t fathom that publications were giving credence to a program that held the form in such contempt. —Literary Hub, 18 May 2026

Not every one of the Padres’ 13 victories that have been earned by scoring the decisive run in the seventh inning or later falls into the category of virtually impossible to fathom. —Kevin Acee, San Diego Union-Tribune, 14 May 2026

Buffie Campbell, executive director of the InterTribal Sinkyone Wilderness Council — co-founded by Priscilla Hunter and one of the groups supporting the bill — said young people wouldn’t be able to fathom the significance of the legislation passing. —Lila Seidman, Los Angeles Times, 10 May 2026

Word History

Etymology

First Known Use

1607, in the meaning defined at intransitive sense 1

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Kids Definition

fathom

1 of 2 noun

fath·​om ˈfat͟h-əm 

: a unit of length equal to six feet (about 1.83 meters) used especially for measuring the depth of water

fathom

2 of 2 verb

1

: to measure by a sounding line

2

: to come to understand

can't fathom why

fathomable

ˈfat͟h-ə-mə-bəl 

adjective