# mass

/ˈmæs/ (US) · /mˈæs/ (UK) · CEFR B2 · Noun

Source: https://englishreference.com/word/mass
Updated: 2026-08-15

## Definition

a large amount of something that has no clear shape. It can also mean the amount of physical matter in an object.

For teachers: a large body of matter with no definite shape; in physics, the quantity of matter in a body regardless of its volume or any forces acting on it.

## Examples

- The clouds formed a dark mass in the sky.
- The doctor found a small mass in the patient's lung during the routine scan.
- In Newtonian physics, mass is treated as a constant property of an object, whereas in relativistic contexts, it is understood to increase as the object approaches the speed of light.

## Usage notes

- Countable when referring to a specific physical lump or growth; uncountable when referring to the general property of matter in physics.

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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.