# immutable

/ˌɪmˈjutəbəɫ/ (US) · /ɪmjˈuːtəbəl/ (UK) · CEFR C1 · Adjective

Source: https://englishreference.com/word/immutable
Updated: 2026-05-20

## Definition

describing something that cannot be changed or fixed. In programming, it means a value or object that stays the same once it is created.

For teachers: incapable of being altered or changed. In a programming context, it describes data structures or values that cannot be modified after their initial creation.

## Examples

- The constant value is immutable.
- Using immutable data structures can help prevent bugs in your code by ensuring that once a value is set, it remains the same.
- Functional programming languages often rely on immutable variables to ensure that the state of the application remains predictable and consistent across different threads of execution.

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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.