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[ik-sten-shuh n] /ɪkˈstɛn ʃən/
an act or instance of extending, lengthening, stretching out, or enlarging the scope of something.
the state of being extended, lengthened, or stretched out.
that by which something is extended or enlarged; an addition:
a four-room extension to a house.
an additional period of time given one to meet an obligation:
My term paper wasn't finished so I asked for an extension.
something that is expandable or can be extended; an extended object:
a table with drop-leaf extensions.
range or scope of extending; degree of extensiveness; extent:
the extension of our knowledge.
an additional telephone that operates on the principal line.
  1. the act of straightening a limb.
  2. the position that a limb assumes when it is straightened.
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.
Compare intension (def 5).
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.
of or relating to extension courses.
Origin of extension
1350-1400; Middle English < Latin extēnsiōn- (stem of extēnsiō). See extensive, -ion
Related forms
extensionality, extensionalism, noun
extensional, adjective
extensionally, adverb
extensionless, adjective
nonextension, noun
nonextensional, adjective
proextension, adjective
superextension, noun
1. contraction. Unabridged
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British Dictionary definitions for extension


the act of extending or the condition of being extended
something that can be extended or that extends another object
the length, range, etc, over which something is extended; extent
an additional telephone set connected to the same telephone line as another set or other sets
a room or rooms added to an existing building
a delay, esp one agreed by all parties, in the date originally set for payment of a debt or completion of a contract
the property of matter by which it occupies space; size
  1. the act of straightening or extending an arm or leg
  2. its position after being straightened or extended
(med) a steady pull applied to a fractured or dislocated arm or leg to restore it to its normal position See also traction (sense 3)
  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
  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 (sense 1a)
  2. conservative extension, a formal theory that includes among its theorems all the theorems of a given theory
Word Origin
C14: from Late Latin extensiō a stretching out; see extend
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
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Word Origin and History for extension

c.1400, from Old French extension (14c.) and directly from Latin extensionem/extentionem (nominative extensio/extentio), noun of action from past participle stem of extendere (see extend). In a concrete sense, "extended portion of something" (a railroad, etc.), from 1852. Telephone sense is from 1906.

Online Etymology Dictionary, © 2010 Douglas Harper
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extension in Medicine

extension ex·ten·sion (ĭk-stěn'shən)
Abbr. ext.

  1. The act of straightening or extending a flexed limb.

  2. A pulling or dragging force exerted on a limb in a distal direction.

The American Heritage® Stedman's Medical Dictionary
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extension in Science
  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.

The American Heritage® Science Dictionary
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extension in Technology

1. filename extension.
2. A feature or piece of code which extends a program's functionality, e.g. a plug-in.

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