extension

American  

[ik-sten-shuhn] / ɪkˈstɛn ʃən /

noun

extensions plural

1. an act or instance of extending, lengthening, stretching out, or enlarging the scope of something.

   Synonyms:

   dilation, increase, enlargement, expansion

   Antonyms:

   contraction

2. the state of being extended, lengthened, or stretched out.

3. that by which something is extended or enlarged; an addition.

   a four-room extension to a house.

   Synonyms:

   continuation, protraction

4. an additional period of time given one to meet an obligation.

   My term paper wasn't finished so I asked for an extension.

   Synonyms:

   delay

5. something that is expandable or can be extended; an extended object.

   a table with drop-leaf extensions.

6. range or scope of extending; degree of extensiveness; extent.

   the extension of our knowledge.

   Synonyms:

   limit

7. an additional telephone that operates on the principal line.

8. Commerce. a written engagement on the part of a creditor, allowing a debtor further time to pay a debt.

9. Physics. that property of a body by which it occupies space.

10. Anatomy.

    1. the act of straightening a limb.

    2. the position that a limb assumes when it is straightened.

11. Surgery. the act of pulling the broken or dislocated part of a limb in a direction from the trunk, in order to bring the ends of the bone into their natural situation.

12. Also called extent.  Logic. the class of things to which a term is applicable, as “the class of such beings as Plato and Alexander” to which the term “man” is applicable.

13. Mathematics. a function having a domain that includes the domain of a given function and that has the same value as the given function at each point in the domain of the given function.

14. Also called file extension.  Computers. one or more characters at the end of a filename, usually following a period, used to indicate the type of file.

15. Manège. the act of bringing or coming into an extended attitude.

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adjective

1. of or relating to extension courses.

extension British  

/ ɪkˈstɛnʃən /

noun

1. the act of extending or the condition of being extended

2. something that can be extended or that extends another object

3. the length, range, etc, over which something is extended; extent

4. an additional telephone set connected to the same telephone line as another set or other sets

5. a room or rooms added to an existing building

6. a delay, esp one agreed by all parties, in the date originally set for payment of a debt or completion of a contract

7. the property of matter by which it occupies space; size

8. 1. the act of straightening or extending an arm or leg

   2. its position after being straightened or extended

9. med a steady pull applied to a fractured or dislocated arm or leg to restore it to its normal position See also traction

10. 1. a service by which some of the facilities of an educational establishment, library, etc, are offered to outsiders

    2. ( as modifier )

       a university extension course

11. logic

    1. the class of entities to which a given word correctly applies: thus, the extension of satellite of Mars is the set containing only Deimos and Phobos Compare intension

    2. a formal theory that includes among its theorems all the theorems of a given theory

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extension Scientific  

/ ĭk-stĕn′shən /

1. Mathematics A set that includes a given and similar set as a subset.

2. Computer Science A set of characters that follow a filename and are separated from it by a period, used to identify the kind of file.

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Other Word Forms

Derived Forms

• extensionalism
  noun
• extensionality
  noun
• nonextension
  noun
• superextension
  noun
• extensional
  adjective
• extensionless
  adjective
• nonextensional
  adjective
• proextension
  adjective
• extensionally
  adverb

Inflected Forms

Nouns

• extensions
  plural

Etymology

Origin of extension

1350–1400; Middle English < Latin extēnsiōn- (stem of extēnsiō ). See extensive, -ion

Explanation

An extension is the act of getting more time, space, or length, like an extension of a deadline that gives you one more day to turn in a paper, or extensions that make your hair look longer. The noun extension comes from the Latin word extendere, meaning “stretch out.” If you’re a great gymnast, you probably have amazing extension — flexible and long-reaching limbs. If someone meets your sister and assumes you will be exactly like her, you might say, "That's a stretch," meaning this person has, by extension, drawn conclusions about you which are somewhat true but not completely accurate.

Example Sentences

See Examples For:

extension extensions

But any extension is unlikely before September because the House of Representatives has already left Washington for its summer recess.

From Barron's ● Jul. 28, 2026

Jalen Brunson left about $113 million on the table when he signed his four-year, $156.5 million contract extension with the Knicks in 2024.

From The Wall Street Journal ● Jul. 26, 2026

Already among the longest-running partnerships in college sports, the extension of the all-sports apparel deal runs through 2036, the school announced Tuesday.

From Los Angeles Times ● Jul. 23, 2026

Tuchel, 52, signed a two-year contract extension in February having been appointed in January 2025 and retains the backing of the FA.

From BBC ● Jul. 20, 2026

He had fed an extension cord through a crack in the screen door, connected to a box fan that blew at his feet.

From "The Line Tender" by Kate Allen

That seat growth would include new licenses for Copilot extensions like GitHub Copilot and Dragon Medical.

From MarketWatch ● Jul. 28, 2026

He appreciates the team that “took a chance on a kid from a little town in southern New Jersey” and signed him to two nine-figure contract extensions.

From Los Angeles Times ● Jul. 10, 2026

Federal employees who disclose such moves beyond that time frame and any extensions granted to them are subject to a $200 fine per late report.

From The Wall Street Journal ● Jul. 2, 2026

Its recipients can legally live and work in the US for up to 18 months, subject to extensions.

From BBC ● Jun. 25, 2026

Anytime we went to a store and I saw a wig or extensions, I would point them out, ever so hopefully.

From "How Dare the Sun Rise" by Sandra Uwiringiyimana

Related Words

• delay
• development
• expansion
• increase
• postponement