index

noun
in·​dex | \ˈin-ˌdeks \
plural indexes or indices\ˈin-​də-​ˌsēz \

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

d : thumb index

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

index

verb
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

Keep scrolling for more

Other Words from index

Verb

indexer noun

Synonyms for index

Synonyms: Noun

hand, indicator, needle, pointer

Synonyms: Verb

catalog (or catalogue), enroll (also enrol), enter, inscribe, list, put down, record, register, schedule, slate

Visit the Thesaurus for More 

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
See More

Recent Examples on the Web: Noun

All three indexes are up more than 4.2 percent for the week, the first time since Nov. 1 that the market benchmarks climbed in three consecutive sessions. Recode Staff, Recode, "Recode Daily: ‘I don’t think Amazon understands how close they are to blowing themselves up’," 29 Nov. 2018 The United States scored the lowest in a United Nations index that ranks how much action each government in the G20 has taken to meet development goals. Alexia Fernández Campbell, Vox, "The G20 summit is a reminder of how little the US is doing for American workers," 26 Nov. 2018 Japan's main stock index, the Nikkei 225, gained 1.1 percent while the Shanghai Composite Index added 0.5 percent. CBS News, "As U.S. tariffs take effect, China says it will retaliate," 6 July 2018 Markets in the Asia-Pacific region were mostly higher Thursday, led by indexes in Australia and Japan. Christopher Whittall, WSJ, "Banks, Utilities Drag European Stocks Lower," 22 Nov. 2018 PurpleAir, a network of air quality monitoring sensors, shows air quality index measurements as dots on a map. Megan Spurrell, Condé Nast Traveler, "California Fires: What to Know If You're Visiting California This Week," 21 Nov. 2018 Manufacturers figured out how to put index systems inside the brake handles. John Timmer, Ars Technica, "How bicycles have changed in the last 25 years," 10 Nov. 2018 Saturday will be mostly sunny and hot, with a high near 95 degrees but a heat index as high as 101. The Courier-Journal, "5 things to know Friday: Yum Center, Papa John's fallout and more," 13 July 2018 During the Big Gig's run this year from June 27 to July 8 (with a day off July 2), there were excessive heat index warnings of over 100 degrees for three days. Piet Levy, Milwaukee Journal Sentinel, "Summerfest in Milwaukee reports lowest attendance in at least 25 years," 13 July 2018

Recent Examples on the Web: Verb

These numbers were indexed to the number of Peloton customers observed in Q1 2017. Rani Molla, Recode, "Peloton now has more U.S. customers than SoulCycle, new data suggests," 3 Dec. 2018 At its core, Google indexes the entire web — some hundreds of billions of pages — using programs called web crawlers. Ryan Nakashima, The Seattle Times, "AP EXPLAINS: How Google search results work," 28 Aug. 2018 Indexing capital gains without indexing interest payments and depreciation would not make the tax system neutral with respect to inflation, which is a sensible goal. Alan S. Blinder, WSJ, "Index Capital Gains, but Not Without Congress’s Consent," 1 Aug. 2018 Of course, Google already has all of that information indexed, whether it’s puppy breeds, restaurant menus, clothing inventory, or foreign languages. Lauren Goode, WIRED, "Lens, Google's Visual Search Tool, Gets Its Most Significant Update Yet," 8 May 2018 At President Reagan’s behest, Congress in the 1980s indexed much of the federal tax code for inflation. Kimberley A. Strassel, WSJ, "Trump Alone Can Cut Taxes," 12 July 2018 The income thresholds are doubled for married couples and indexed to inflation. Kathleen Pender, SFChronicle.com, "Dozens of millionaires fled California after 2012 tax increase, study says," 6 July 2018 Congress initially made 90 percent of total income eligible for Social Security taxes, but indexed it to average wage growth. Ken Fisher, USA TODAY, "4 Social Security myths and the reasons why they're overblown," 24 June 2018 Each event is indexed so a particular play can later be viewed with a single tap. Tom Simonite, WIRED, "Apple's Plans to Bring Artificial Intelligence to Your Phone," 6 June 2018

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.

See More

First Known Use of index

Noun

1561, in the meaning defined at sense 3a

Verb

1720, in the meaning defined at transitive sense 1a

History and Etymology for index

Noun

Latin indic-, index, from indicare to indicate

Keep scrolling for more

Learn More about index

Statistics for index

Last Updated

10 Dec 2018

Look-up Popularity

Time Traveler for index

The first known use of index was in 1561

See more words from the same year

Keep scrolling for more

More Definitions for index

index

noun

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

index

verb

English Language Learners Definition of index

: 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

index

noun
in·​dex | \ˈin-ˌdeks \
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.

index

verb
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.

Keep scrolling for more

index

noun
in·​dex | \ˈin-ˌdeks \
plural indexes or indices\-​də-​ˌsēz \

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

index

noun
in·​dex

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

Keep scrolling for more

More from Merriam-Webster on index

Rhyming Dictionary: Words that rhyme with index

Thesaurus: All synonyms and antonyms for index

Spanish Central: Translation of index

Nglish: Translation of index for Spanish Speakers

Britannica English: Translation of index for Arabic Speakers

Britannica.com: Encyclopedia article about index

Comments on index

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

WORD OF THE DAY

having a pattern of small flowers

Get Word of the Day daily email!

Test Your Vocabulary

Find the Cousins

  • a-large-tree-with-many-branches
  • Which pair shares a common word ancestor?
Name That Thing

Test your visual vocabulary with our 10-question challenge!

TAKE THE QUIZ
Word Winder's CrossWinder

Test Your Knowledge - and learn some interesting things along the way.

TAKE THE QUIZ

Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!