ex·​ten·​sion | \ik-ˈsten(t)-shən \

Definition of extension 

1a : the action of extending : state of being extended

b : an enlargement in scope or operation tools are extensions of human hands

2a : the total range over which something extends : compass

b : denotation sense 4

3a : 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

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

7a : 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

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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.
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Recent Examples on the Web

Most people don't have magically long blonde hair, but thankfully there are hair extensions to pull off the princess's trademark style. Blake Bakkila, Good Housekeeping, "These 3 DIY Disney Couples Costumes Are Perfect (and Easy!) for Halloween," 25 Oct. 2018 Storage is found throughout, with full extension drawers and fancy aluminum trim. Megan Barber, Curbed, "Glamorous vintage camper is your midcentury dream home on wheels," 18 Oct. 2018 And because Vivaldi and Chrome share some DNA under the hood, many of Chrome’s best features, including its expansive suite of apps and extensions, are available on Vivaldi as well. Avery Thompson, Popular Mechanics, "A Year Ago I Ditched Chrome For Vivaldi and Never Looked Back," 26 Sep. 2018 Drives can be connected to existing M.2 slots on motherboards using an extension cable. Gordon Mah Ung, PCWorld, "Intel's 905P Optane reaches a tempting 1.5TB, but drive prices remain high," 21 Sep. 2018 Former Bull Jimmy Butler has rejected the Timberwolves’ four-year, $110-million extension offer, according to Darren Wolfson of St. Paul TV station KSTP. Chicago Tribune Staff, chicagotribune.com, "Report: Jimmy Butler rejects Timberwolves' $110-million extension offer," 13 July 2018 To register, send an email to edward.lafferty@ssa.gov or call 866-398-3469, extension 29305. Erin Arvedlund, Philly.com, "Do ESG investments outperform? One investor says 'no way'," 9 July 2018 That's the biggest revelation in the amended 2017 campaign finance reports Pastor filed Friday afternoon after requesting two previous extensions to make corrections. Sharon Coolidge, Cincinnati.com, "At last, some answers about Cincinnati Councilman Jeff Pastor's campaign finances," 8 July 2018 FedEx last year agreed to a 10-year extension, and the bonus pool for the postseason now is $60 million (along with $10 million in bonus money for the regular season). Doug Ferguson, The Seattle Times, "FedEx Cup to offer $15 million to winner next year," 18 Sep. 2018

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'extension.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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First Known Use of extension

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

History and Etymology for extension

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

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Statistics for extension

Last Updated

3 Dec 2018

Look-up Popularity

Time Traveler for extension

The first known use of extension was in the 15th century

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More Definitions for extension


ex·​ten·​sion | \ik-ˈsten-shən \

Kids Definition of extension

1 : the act of making something longer or greater extension of the sail

2 : an increase in length or time

3 : a part forming an addition or enlargement


ex·​ten·​sion | \ik-ˈsten-chən \

Medical Definition of extension 

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 of extension 

: an increase in length of time specifically : an increase in the time allowed under an agreement

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Comments on extension

What made you want to look up extension? Please tell us where you read or heard it (including the quote, if possible).


to enclose within walls

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