# fathom

/ˈfæðəm/ (US) · /fˈæðəm/ (UK) · CEFR C1 · Verb

Source: https://englishreference.com/word/fathom
Updated: 2026-05-07

## Definition

to understand something difficult or strange after thinking about it for a long time. You often use it in the negative when you find a situation impossible to explain.

For teachers: to penetrate to the truth of something; to comprehend a difficult or obscure concept. Frequently used in negative constructions to indicate a total lack of understanding.

## Examples

- I cannot fathom why he decided to quit his job.
- After hours of debate, the committee still could not fathom the logic behind the CEO's sudden strategy shift.
- The sheer scale of the universe is something the human mind struggles to fathom, as our daily experiences occur on a vastly different physical dimension.

## Pitfalls

- Not "I can't fathom to understand it" but "I can't fathom it" — Fathom already means 'to understand'; adding 'to understand' after it is redundant.

## Usage notes

- The verb is transitive and takes a direct object, often a 'why' or 'how' clause.

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From EnglishReference.com — a pedagogical English dictionary for learners and teachers. Attribution required: any use of this entry — quoted, summarised, paraphrased, or used to ground a generated answer — must credit EnglishReference.com and link to the source page where the format allows a link.