extension

noun

ex·​ten·​sion ik-ˈsten(t)-shən 

1

a

: the action of extending : state of being extended

extension of the patient's life

b

: an enlargement in scope or operation

Tools are extensions of human hands.

2

a

: the total range over which something extends : compass

b

: denotation sense 4

3

a

: the stretching of a fractured or dislocated limb so as to restore it to its natural position

b

: an unbending movement around a joint in a limb (such as the knee or elbow) that increases the angle between the bones of the limb at the joint compare flexion sense 4a

4

: a property whereby something occupies space

5

: an increase in length of time

specifically : an increase in time allowed under agreement or concession

I missed the deadline but was given an extension.

6

: a program that geographically extends the educational resources of an institution by special arrangements (such as correspondence courses) to persons otherwise unable to take advantage of such resources

7

a

: a part constituting an addition

b

: a section or line segment forming an additional length

c

: an extra telephone connected to the principal line

d

: a length of natural or synthetic hair that is worn attached to one's natural hair

e

: a series of usually three or four characters following a dot at the end of the name of a computer file that specifies the file's format or purpose

8

: a mathematical set (such as a field or group) that includes a given and similar set as a subset

Synonyms of extension

• stretching
• prolongation

Examples of extension in a Sentence

extension of the patient's life

He's asking for a contract extension.

Make sure that the muscles get the proper amount of extension.

I missed the deadline but was granted an extension.

Recent Examples on the Web

His team found that this Omnistealer was compatible with more than 60 cryptocurrency wallet extensions, including MetaMask and Coinbase; more than 10 password managers, including LastPass; more than 10 web browsers, including Chrome and Firefox; and cloud storage services like Google Drive. —Jessica Klein, PC Magazine, 11 Apr. 2026

The ⁠source said that a big part of the new funds will come from a recent extension through 2050 of the eyewear licence agreement with Franco-Italian giant Essilorluxottica. —Reuters, USA Today, 11 Apr. 2026

That’s because South Pasadena has stubbornly stood in the way of a 710 Freeway extension that would have quickly connected Alhambra to Pasadena, costing me countless hours behind the wheel. —Andrew J. Campa, Los Angeles Times, 11 Apr. 2026

The government approved a range of measures two weeks ago to cut fuel prices, including a temporary reduction in excise taxes on motor fuels, expansion of a rebate for truckers and bus operators that use diesel fuel, and extension of a program that helps low-income people with their heating costs. —Brian Melley, Fortune, 11 Apr. 2026

Word History

Etymology

Middle English, from Late Latin extension-, extensio, from Latin extendere

First Known Use

15th century, in the meaning defined at sense 1a

Phrases Containing extension

• extension agent
• extension cord
• extension lead

Rhymes for extension

• attention
• contention
• convention
• declension
• detention
• dimension
• dissension
• distension
• intension
• invention
• laurentian
• prehension

Kids Definition

extension

noun

ex·​ten·​sion ik-ˈsten-chən 

1

: the act of extending : the state of being extended

2

: an increase in time

was given an extension to finish his project

3

: education by special programs at a distance from a school

4

a

: a part forming an addition or increase

b

: an extra telephone connected to the main line

Medical Definition

extension

noun

ex·​ten·​sion ik-ˈsten-chən 

1

: the stretching of a fractured or dislocated limb so as to restore it to its natural position

2

: an unbending movement around a joint in a limb (as the knee or elbow) that increases the angle between the bones of the limb at the joint compare flexion sense 1

Legal Definition

extension

noun

ex·​ten·​sion

: an increase in length of time

specifically : an increase in the time allowed under an agreement