in·​dex | \ ˈin-ˌdeks How to pronounce index (audio) \
plural indexes or indices\ ˈin-​də-​ˌsēz How to pronounce indices (audio) \

Definition of index

 (Entry 1 of 2)

1 : a list (as of bibliographical information or citations to a body of literature) arranged usually in alphabetical order of some specified datum (such as author, subject, or keyword): such as
a : a list of items (such as topics or names) treated in a printed work that gives for each item the page number where it may be found
b : a list of publicly traded companies and their stock prices
c : a bibliographical analysis of groups of publications that is usually published periodically
2a : a number (such as a ratio) derived from a series of observations and used as an indicator or measure specifically : index number
b : the ratio of one dimension of a thing (such as an anatomical structure) to another dimension
3a : a device (such as the pointer on a scale or the gnomon of a sundial) that serves to indicate a value or quantity
b : something (such as a physical feature or a mode of expression) that leads one to a particular fact or conclusion : indication
4 plural usually indices : a number or symbol or expression (such as an exponent) associated with another to indicate a mathematical operation to be performed or to indicate use or position in an arrangement 3 is the index of the expression {latex}\sqrt[3]{5}{/latex} to indicate the cube root of 5
5 : a character ☞ used to direct attention to a note or paragraph

called also fist

6 : a list of restricted or prohibited material specifically, capitalized : a formerly published list of books the reading of which was prohibited or restricted for Roman Catholics by the church authorities


indexed; indexing; indexes

Definition of index (Entry 2 of 2)

transitive verb

1a : to provide with an index
b : to list in an index all persons and places mentioned are carefully indexed
2 : to serve as an index of
3 : to regulate (wages, prices, interest rates, etc.) by indexation

intransitive verb

: to index something

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Other Words from index


indexer noun

Examples of index in a Sentence

Noun Look up the recipe for potato soup in the index. Potato soup is listed under “soup” in the index. The card catalog is an index to the materials in the library. the index on a scale Verb This search engine has indexed hundreds of millions of Web sites. indexed all the books in the library by category
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Recent Examples on the Web: Noun The index, which is heavily weighted with technology stocks, also notched a record high on Tuesday. Alex Veiga,, "Stocks extend rally, sending S&P 500, Nasdaq to all-time highs," 5 Feb. 2020 Dallas home prices are at record levels in the Case-Shiller index, up more than 70% from 2009. Steve Brown, Dallas News, "Dallas-area home prices up 2.8% in nationwide study," 28 Jan. 2020 In Hong Kong, the Hang Seng dropped 1.5%, while the Shanghai Composite index declined 2.8%. Aimee Picchi, CBS News, "Coronavirus in China: How the outbreak could impact investors," 23 Jan. 2020 But for economics enthusiasts the fast-food dish of choice will always be a McDonald’s Big Mac, whose price underlies the Big Mac index, The Economist’s light-hearted guide to global exchange rates. The Economist, "Daily chart What can burgers tell us about foreign-exchange markets?," 15 Jan. 2020 Sixty tech companies released transparency reports in 2018, according to its index, most of them in North America. Louise Matsakis, Wired, "TikTok's First Transparency Report Doesn't Tell the Full Story," 3 Jan. 2020 Hong Kong’s benchmark Hang Seng Index and the Shanghai Composite index saw their best one-day gains in months. Fortune, "The Case of Liu vs. Liu," 14 Dec. 2019 The Shanghai Composite index lost 0.6% to 2,991.05 while the Hang Seng in Hong Kong edged 0.1% lower to 26,503.93. San Diego Union-Tribune, "World shares mostly higher after wobbly day on Wall Street," 15 Oct. 2019 Over the past year, shares in H&M have gained more than 35%, beating the OMX Stockholm index, which is up 19%. Anton Wilen, Fortune, "H&M’s first female CEO takes over from founding family scion after fast-fashion pioneer struggles," 30 Jan. 2020 Recent Examples on the Web: Verb The records, now indexed, include most of the major churches and synagogues in the city, structures such as League Park and the Gordon Square theater and other major commercial buildings. Robert Higgs, cleveland, "Martin Hauserman has made a career as the keeper of Cleveland’s history, documenting city government and life of the people," 24 Jan. 2020 And when the fingertips merely shear, and yet perceive, a dip so shallow, the brain is brought up short, with no way to index the experience. Virginia Heffernan, Wired, "The Unbearable Softness of Engineered Fabrics," 21 Jan. 2020 New articles on wikiHow are de-indexed from search results and blurred out for casual readers, visible only to logged-in contributors until they’ve been reviewed. Kaitlyn Tiffany, The Atlantic, "How to Make a Website," 11 Nov. 2019 Simply stated, your Social Security retirement benefit is based on your average monthly income, indexed for inflation, using a 35-year base of earnings. Tom Margenau, Dallas News, "Earnings after retirement: Will they increase your Social Security check?," 2 Feb. 2020 The higher Ohio wage would also be indexed to inflation. Olivera Perkins, cleveland, "Ohio’s minimum wage ranks near bottom among states with rates higher than federal minimum," 19 Jan. 2020 Those were indexed against precise metrics about the vehicle’s movement. New York Times, "Avoiding Carsickness When the Cars Drive Themselves," 17 Jan. 2020 The field guide takes an innovative approach to indexing the Sand Sheet’s plant life in a way that is simple for those who have not taken a college botany course. Matt Wyatt,, "South Texas Sand Sheet’s unique treasures uncovered," 16 Jan. 2020 Many of them are the result of increases that have been implemented in phases over the past few years, or indexed to inflation. Washington Post, "Minimum wage increases fueling faster wage growth for those at the bottom," 2 Jan. 2020

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'index.' 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 index


1561, in the meaning defined at sense 3a


1720, in the meaning defined at transitive sense 1a

History and Etymology for index


Latin indic-, index, from indicare to indicate

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Time Traveler for index

Time Traveler

The first known use of index was in 1561

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Statistics for index

Last Updated

19 Feb 2020

Cite this Entry

“Index.” Dictionary, Merriam-Webster, Accessed 29 Feb. 2020.

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More Definitions for index



Financial Definition of index

What It Is

An index is a statistical aggregate that measures change. In finance, they usually refer to measures of stock market performance or economic performance.

How It Works

Let's say we want to measure the stock price performance of the widget industry. There are currently four public companies that make widgets in the United States: Company A, Company B, Company C, and Company D. In the year 2000, when we started caring about the seedling U.S. widget industry, the four companies' stock prices were as follows:

Company A     $10
Company B     $8
Company C     $12
Company D     $25

Total $55

To create an index, we simply set the total ($55) in the year 2000 equal to 100 and measure any future periods against that total. For example, let's assume that in 2001 the stock prices were:

Company A     $4
Company B     $38
Company C     $12
Company D     $24

Total $78

Because $78 is 41.82% higher than the 2000 base, the index is now at 141.82. Every day, month, year, or other period, the index can be recalculated based on current stock prices.

Note that this index is weighted by stock price (i.e., the larger the stock price, the more influence it has on the index). Indexes can be weighted by shares outstanding, market capitalization, or any other factors the indexer chooses. When new companies go public or existing companies founder, the indexer may add or delete companies from the index or "reweight" the index to accommodate stock splits or other factors.

Why It Matters

In finance, the most significant numbers in any given day's news are usually market indices. The Dow Jones Industrial Average is probably the best-known and most widely followed financial index in the world. It consists of 30 The definition of index on InvestingAnswersof the largest publicly traded firms in the United States. The S&P 500 Index is also very common, comprising over 70% of the total market cap of all stocks traded in the U.S. The Nasdaq Composite is a broad market index that encompasses about 4,000 issues traded on the Nasdaq National Market -- virtually every firm that trades on the exchange.

Indices are also used to gauge activity in an economy. Perhaps the best known economic index in the United States is the CPI, or Consumer Price Index, which measures inflation.

Source: Investing Answers


How to pronounce index (audio)

English Language Learners Definition of index

 (Entry 1 of 2)

: an alphabetical list at the end of a book that shows the page where each thing in the list can be found
: a group of related things that are in alphabetical or numerical order
: a sign or number that shows how something is changing or performing : a number that indicates changes in the level of something (such as a stock market) when it rises or falls



English Language Learners Definition of index (Entry 2 of 2)

: to provide an index for (something, such as a book)
: to list or include (something) in an index
: to link wages, benefits, etc., to a measurement of changes in the price of goods and services so that they increase at the same rate


in·​dex | \ ˈin-ˌdeks How to pronounce index (audio) \
plural indexes or indices\ ˈin-​də-​ˌsēz \

Kids Definition of index

 (Entry 1 of 2)

1 : a list of names or topics (as in a book) given in alphabetical order and showing where each is to be found
2 : pointer sense 1 the index on a scale
3 : sign entry 1 sense 3, indication Prices are an index of business conditions.


indexed; indexing

Kids Definition of index (Entry 2 of 2)

1 : to provide (as a book) with an index
2 : to list in an index The topics are indexed.

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in·​dex | \ ˈin-ˌdeks How to pronounce index (audio) \
plural indexes or indices\ -​də-​ˌsēz How to pronounce indices (audio) \

Medical Definition of index

2 : a list (as of bibliographical information or citations to a body of literature) arranged usually in alphabetical order of some specified datum (as author, subject, or keyword) Index Medicus of the United States National Library of Medicine
3a : a ratio or other number derived from a series of observations and used as an indicator or measure (as of a condition, property, or phenomenon) physiochemical indexes of the urine, the blood, and the gastric juiceJournal of the American Medical Association
b : the ratio of one dimension of a thing (as an anatomical structure) to another dimension — see cephalic index, cranial index



Legal Definition of index

 (Entry 1 of 2)

: a numerical measure or indicator (as of inflation or economic performance) — see also consumer price index

Legal Definition of index (Entry 2 of 2)

: to link (as wages, rates, or investments) to an index under the contract wages were indexed to inflation

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More from Merriam-Webster on index

Thesaurus: All synonyms and antonyms for index

Rhyming Dictionary: Words that rhyme with index

Spanish Central: Translation of index

Nglish: Translation of index for Spanish Speakers

Britannica English: Translation of index for Arabic Speakers Encyclopedia article about index

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