# extension

/ɪkˈstɛnʃən/ (US) · /ɛkstˈɛnʃən/ (UK)

Source: https://englishreference.com/word/extension
Updated: 2026-06-19

## Senses

### 1. extra time

noun · CEFR B2

more time given to finish a task or a project.

For teachers: an additional period of time allowed for the completion of a task, often beyond an original deadline.

- The professor gave me a two-day extension on my essay because I was sick.
- The project manager requested a formal extension of the deadline, citing unforeseen delays in the supply chain that made the original schedule impossible.

### 2. building addition

noun · CEFR B2

a new room or part that is added to an existing building.

For teachers: a structural addition to an existing building that increases its total floor area or volume.

- They are building a kitchen extension to make more room for the family.
- The planning committee approved the rear extension on the condition that the materials matched the original Victorian brickwork.

### 3. phone number

noun · CEFR B2

a short set of numbers used to reach a specific person in a large office.

For teachers: a subsidiary telephone line connected to a main switchboard, identified by a specific numerical code.

- If you need to speak to the manager, call the main office and ask for extension 402.
- The directory lists the direct extensions for every department head, allowing clients to bypass the automated reception menu.

### 4. software/computing

noun · CEFR B2

a small program you add to a web browser or app to give it new features.

For teachers: a software module that adds specific features or functionality to an existing computer program or browser.

- I installed a browser extension that blocks annoying advertisements.
- The developer released a security extension designed to encrypt sensitive data before it is uploaded to the cloud storage service.

### 5. hair or nails

noun · CEFR B2

extra pieces of hair or material added to your own to make them look longer.

For teachers: artificial lengths of hair or synthetic material attached to a person's natural hair or nails for aesthetic purposes.

- She spent three hours at the salon getting hair extensions for the wedding.
- The stylist recommended high-quality silk extensions to ensure the final look appeared natural and blended seamlessly with the client's own hair.

Usage: Usually used in the plural form 'extensions'.

### 6. stretching a limb

noun · CEFR C1 · Technical

the act of straightening a part of your body, like an arm or a leg.

For teachers: the movement by which the two ends of any jointed part are drawn away from each other; the straightening of a limb.

- The physical therapist told him to focus on the full extension of his knee.
- Post-operative recovery protocols emphasize the gradual restoration of full extension in the elbow joint to prevent permanent stiffness.

### 7. file type

noun · CEFR B2

the letters at the end of a computer file name that show what kind of file it is.

For teachers: a suffix consisting of a period and several characters at the end of a filename, indicating the file format.

- Make sure you save the document with a .pdf extension so everyone can open it.
- The operating system uses the file extension to determine which application should be launched by default when the user double-clicks the icon.

## Examples

- I asked my boss for a two-day extension on the report.
- The homeowners decided to build a kitchen extension rather than moving to a larger house.
- The university granted an extension to all students affected by the campus-wide power outage, ensuring that no one was unfairly penalised for the technical failure.

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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.