English Reference

Word

extension

Phoneticsex·ten·sion, stress on the second syllable

US/ɪkˈstɛnʃən/

UK/ɛkstˈɛnʃən/

Definitions

01extra time

B2 · Upper Intermediate Countable noun

n. more time given to finish a task or a project.

n. 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.”

Synonyms

prolongationdelay

02building addition

B2 · Upper Intermediate Countable noun

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

n. 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.”

03phone number

B2 · Upper Intermediate Countable noun

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

n. 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.”

Synonyms

internal line

04software/computing

B2 · Upper Intermediate Countable noun Computing

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

n. 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.”

Synonyms

add-onplugin

05hair or nails

B2 · Upper Intermediate Countable noun

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

n. 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'.

Synonyms

06stretching a limb

C1 · Advanced Uncountable noun Medicine Technical

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

n. 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.”

Synonyms

Antonyms

07file type

B2 · Upper Intermediate Countable noun Computing

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

n. 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.”

Synonyms

Collocations

Common phrases and expressions where native English speakers use the word “extension” in context.

Verb

01. consider extension

“The committee will consider an extension of the deadline if you provide a valid reason.”

verb + noun

Adjective

02. natural extension

“This new project is a natural extension of the research we started last year.”

adj + noun

Noun

03. extension lead

“We need an extension lead to reach the power socket on the other side of the room.”

noun + noun

Real-World Examples

“Despite signing a contract extension in November 2024, the series reveals how close Guardiola came to not renewing his deal.”
BBC News 17 Aug 2026
“Watching the state’s political class focus on cancer, and by extension, water quality, has been a curious experience, since it’s been a concern of theirs for more than a decade, said Smith.”
The Guardian 16 Aug 2026

Etymology

From Middle English extensioun, from Old French estension, from Latin extensiō, extensiōnem.

Etymology adapted from Wiktionary, available under CC BY-SA 4.0.

Word family

NOUN

extension(B2)

ADJECTIVE

Domains

ComputingEducationFinanceGrammarLinguisticsLogicMathematicsMedicine

This entry

Exam level
CambridgeCambridgeCambridge English QualificationsThe exam suite from Cambridge University Press & Assessment, from A1 Movers up to C2 Proficiency. The benchmark names double as CEFR labels.B2 FirstIELTSIELTSInternational English Language Testing SystemThe 0–9 band test co-owned by the British Council, IDP, and Cambridge. Used for university entry, work, and migration.5.5–6.5TOEFL iBTTOEFL iBTTest of English as a Foreign Language, Internet-Based TestETS's academic English test, the standard route for US university admissions. Scored 0–120, with a 1–6 scale since 2026.1–6 scale: 4.0–4.572–94TOEICTOEICTest of English for International CommunicationETS's workplace English test, big in Japan and Korea. Listening & Reading scores 10–990 and tops out at C1.785–944
Frequency
Common
Level
B2 · Upper IntermediateOxford
Updated

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English Reference