extension
Pluralextensions
- 1The act of stretching something out or enlarging it in length, width, or time.
The extension of the contract gave both sides more time to negotiate.
Stretching promotes the extension of muscles beyond their resting length.
Similarlengthening, prolongation, expansion, stretching, enlargement
Oppositeshortening, contraction, reduction, curtailment
Note
The broad meaning the specialized ones branch from. It came into English as Middle English extensioun, by way of Old French estension, from Latin extensiō. It names both a process and a thing you can be given or build: a house undergoes an extension, and a student is allowed an extension of two weeks. When the extra is time, of introduces its length.
- 2A written agreement by a creditor granting a debtor additional time to repay a debt.
The creditor granted a three-month extension on the overdue invoice.
Without an extension in writing, the debtor risked defaulting on the loan.
Similardeferral, postponement, deferment, reprieve
Note
Banking puts the weight on the paper. The creditor commits in writing to wait, and that separates it from a loose promise of more time. Extensions are granted on a debt, loan or invoice and usually carry a stated length, as in a three-month extension. A properly granted one keeps the original term from being treated as in default.
- 3
- 4A short numerical code that directs a call to a specific telephone within a larger network.
Please call the front desk and ask for extension 210.
Each department has its own extension on the office phone system.
Note
Office telephones have a vocabulary of their own. The number follows the noun, like a room number, so you ask for extension 210. An extension belongs to a private branch exchange, which routes internal calls among handsets that share one outside number. Each department or desk usually has its own.
- 5In computing, an add-on piece of software that a user can choose to install to give an application extra features.
A browser extension can translate web pages into your language automatically.
Developers released an extension that adds dark mode to the editor.
Note
Software's other extension, easily confused with the filename suffix: this one is a program, not a label. It plugs into a host application through a defined interface and adds features without changing the application's core, as a browser extension does. You install or disable it; you never type it at the end of a filename.
- 6Ellipsis of file extension.
Files with a .zip extension are compressed to save space.
The program refused to open a file with an unfamiliar extension.
Note
The characters at the tail of a filename tell the system what a file contains and which software opens it. The suffix itself works as a modifier before the noun, as in the .txt extension or a .zip extension, and the dot is usually written. PC Mag warned in 1989 that data files plotted with error bars must carry an .ERR extension or the system would crash.
- 7An outgrowth or added part that increases what something is able to do.
The robotic arm acts as an extension of the surgeon's own reach.
Critics saw the new policy as an extension of earlier reforms.
Similarcontinuation, outgrowth, expansion, development
Note
Mostly figurative, and almost always built as an extension of something: parents who treat children as an extension of themselves, or research that is an extension of a mentor's work. Adjectives such as virtual and natural often sharpen it. In criticism it implies the thing has no independence: Mitzel, writing in Gay Community News in 1978, called small-town public schools virtual extensions of each town's chief religion.
- 8Clipping of hair extension, nail extension, or eyelash extension.
Her stylist matched the extension to her natural hair color.
One eyelash extension came loose after a week.
Note
A salon word that lives mostly in the plural: people get extensions and have their extensions done. One clipping serves three compounds, hair, nail and eyelash extension, and the setting makes clear which is meant. Hair extensions are lengths of hair attached to one's own to make it longer.
- 9A strength exercise in which an arm or leg is straightened while working against a weight or other resistance.
The trainer programmed a knee extension to strengthen her quads.
A slow, controlled extension reduces strain on the joint.
Note
A gym term usually named by the joint or muscle it works: a knee extension loads the quadriceps, and a triceps extension works the back of the arm. It is a single-joint exercise that moves a limb from bent to straight. It is best done slowly and under control to spare the joint.
- 10University programs aimed at the wider community, usually adults, who are not enrolled as full-time students.
She earned a certificate through the university's extension without ever enrolling full time.
The extension runs weekend workshops aimed at working professionals.
Note
Often the name of a university unit as much as its courses: the extension may run weekend workshops and award certificates. Its students are typically working adults rather than full-time enrolled ones. The teaching usually sits outside the standard degree structure.
- 11The condition or state of being extended in space or time.
At full extension, the telescope brought distant stars into focus.
After the injury, his knee would not reach full extension, so he walked with a slight limp.
Similarstretch
Oppositeflexion
Note
Where the act of extending is the movement, this is the position held at the end of it: full extension, the point at which a knee or a telescope will go no further. Thomas Browne, in Pseudodoxia Epidemica, uses it of muscles kept stretched to maintain the body at length. For him, simply standing still was a kind of motion.
- 12The stretching of a broken bone along its length so its fragments are drawn back into a single straight line.
Before applying the cast, the surgeon performed extension to align the shattered fragments.
Traction provides continuous extension that keeps the bone fragments straight while they heal.
Note
In fracture care the word names a pull, not a position. Traction is applied along the length of the bone to draw displaced fragments apart and back into line before a cast or splint holds them. It is a step in reducing a fracture. Do not confuse it with the straightening of a limb in the gym exercise.
- 13The property of a body whereby it occupies a portion of space, and by analogy a stretch of time.
For Descartes, extension is the defining property of physical substance.
Two solid objects cannot share the same extension in space at the same moment.
Note
A philosopher's word for taking up room: anything with a body has extension because it fills some portion of space. The idea carries over to time, and spatiotemporal extension covers both. Keep it apart from the range a term covers. Here extension is a physical property of the thing itself, not a measure of how many things a word applies to.
- 14In fencing, a simple offensive action in which the weapon arm is straightened forward toward the opponent.
The coach drilled the extension until each fencer could threaten without committing fully.
He scored by following his extension with a swift lunge.
Note
In fencing the arm moves first. Straightening the weapon arm presents the point and threatens a valid target before the legs commit. It usually opens an attack and is followed by a lunge or flèche, so a fencer can menace without yet closing the distance. Coaches drill it as the foundation of every simple attack.
- 15The range of objects that a concept or general term applies to: its breadth of reference, the correlative of intension.
The term 'mammal' has a broader extension than 'dog,' which it includes.
Logicians distinguish a term's extension from its intension, or defining content.
Similardenotation
Oppositeintension
Note
One half of a classic pair: extension is how far a term reaches, and intension is what it means. As intension grows, extension typically narrows, so 'dog' says more than 'mammal' and covers less. Frege gave the extension of a concept its own name, a course of values, as Edwin Mares explains in the Stanford Encyclopedia of Philosophy. For the formal set a predicate picks out, see the logician's version.
- 16A widening of a word's meaning, so that it comes to refer to more than it originally did.
The shift of 'cool' from a temperature word to a term of approval is a clear case of extension.
Linguists describe how extension gradually loosens the original limits of a word's meaning.
Similarbroadening, widening, generalization
Oppositenarrowing, specialization, restriction
Note
A term for change over time, where a term's range is a snapshot. A word's meaning widens until it covers more than it once did, as cool spread from temperature to approval. Its opposite is narrowing, or restriction. Linguists also say widening or broadening; extension is the more technical label.
- 17In logic, the set of argument tuples that satisfy a given predicate: the things of which it is true.
The extension of the predicate 'is red' contains every red object.
Two predicates with the same extension are coextensive, even when they differ in meaning.
Oppositeintension
Note
The logician's formal version of a term's range. A predicate's extension is the set of things it is true of. For a predicate with two or more places, those things are ordered tuples rather than single objects. Predicates that share an extension are coextensive even when their meanings differ, so extension alone cannot capture meaning.
- 18In group theory, a short exact sequence 1→H→E→G→1, or the middle group E that contains H as a normal subgroup with quotient G.
An extension of G by H places H as a normal subgroup of E whose quotient is G.
Central extensions, where H lies in the center of E, arise throughout the theory of projective representations.
Note
The preposition carries the structure here. An extension of G by H places H inside as a normal subgroup and G outside as the quotient, so the phrase reads in the opposite order from the sequence 1→H→E→G→1. Either the whole sequence or the middle group E may be called the extension. Equivalence classes of such sequences are classified cohomologically, and central extensions are the case met in projective representations.
- 19In homological algebra, a short exact sequence 0→B→E→A→0, or the middle object E that contains B as a subobject with quotient A.
An extension of A by B fits B inside E so that the quotient is A.
Extensions of one module by another are classified by the Ext functor.
Note
The same pattern carried into abelian categories, where modules and similar objects replace groups and the ends of the sequence are 0 rather than 1. The word order works as in the group-theory meaning: an extension of A by B holds B as a subobject and has A as its quotient. Equivalence classes of such extensions are parametrized by the derived functor Ext¹(A,B).
- 20In ring theory, the ideal in the target ring generated by the image of a given ideal under a ring homomorphism.
The extension of a prime ideal need not remain prime in the larger ring.
Computing the extension of an ideal along an inclusion is a routine step in localization.
Note
Ring theory uses it for pushing an ideal forward along a homomorphism f: R→S. You take the image f(I) and generate an ideal in S, written IS. Its partner is contraction, which pulls ideals of S back to R. Properties do not always survive the trip: the extension of a prime ideal need not be prime.
- 21In Bantu languages, a derivational morpheme suffixed to a verb root that alters its meaning or the arguments it takes.
The applicative extension adds a beneficiary argument to the verb.
Swahili stacks several extensions onto a single verb root.
Note
A Bantu grammarian's term for the suffixes that sit between a verb root and its final vowel, among them the applicative, causative, passive and reciprocal. Each changes the verb's valency or the kind of action it describes. They combine productively in fixed orders, which is how Swahili stacks several onto a single root.
Practice
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Origin
It comes from Middle English "extensioun", from Old French "estension", which in turn derives from Latin "extensiō, extensiōnem".