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# index

noun in·dex \ ˈin-ˌdeks \
|Updated on: 6 Aug 2018

## Definition of index

plural indexes or indices\ˈin-də-ˌsēz\
1 a : 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
2 : 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
c : a bibliographical analysis of groups of publications that is usually published periodically
d : a list of publicly traded companies and their stock prices
3 : 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
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 : a number (such as a ratio) derived from a series of observations and used as an indicator or measure; specifically
b : the ratio of one dimension of a thing (such as an anatomical structure) to another dimension

## Examples of index in a Sentence

1. Look up the recipe for potato soup in the index.

2. Potato soup is listed under “soup” in the index.

3. The card catalog is an index to the materials in the library.

4. the index on a scale

## Recent Examples of index from the Web

• Another, Richard Dunkel, began his own process in 1929 with a stack of index cards and had carved out a niche in the industry, as had Herman Matthews, who began rating college football teams in the late 1940s while in high school.
• Heat index values could approach 100 degrees on Independence Day and again on Thursday, the Weather Service says.
• The National Weather Service has forecasted a high in the mid-90s for the city Saturday, with heat index values as high as 106.
• The Russell 2000 index of small-cap stocks rose 0.5 percent to a record 1,692.46.
• Ramirez Rozzi, however, was lucky enough to have access to records of births since 1980 kept on index cards by nuns at the Catholic mission’s medical center in Moange-le-Bosquet, where more than 800 Baka now live in scattered settlements.
• Such funds have become less popular, especially among younger investors, who have flocked to lower-cost index funds.
• His team brainstormed ideas on 3-by-5 index cards, coming up with a series of prototype arrangements strikingly similar to what was built.
• Each of them has outperformed the stock index over the past year.

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.

## Origin and Etymology of index

Latin indic-, index, from indicare to indicate

## index Synonyms

###### Related Words

dial, face, gauge (also gage);

2

verb

## Definition of index

indexed; indexing; indexes
1 a : 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
: to index something

noun

## Examples of index in a Sentence

1. This search engine has indexed hundreds of millions of Web sites.

2. indexed all the books in the library by category

## Recent Examples of index from the Web

• At President Reagan’s behest, Congress in the 1980s indexed much of the federal tax code for inflation.
• The income thresholds are doubled for married couples and indexed to inflation.
• Congress initially made 90 percent of total income eligible for Social Security taxes, but indexed it to average wage growth.
• Each event is indexed so a particular play can later be viewed with a single tap.
• European earnings have increased since then, but the U.S. has grown much faster—with the gap in earnings per share between MSCI’s USA and Europe indexes ballooning to a 30-year high, according to Mislav Matejka, equity strategist at JPMorgan.
• Emails and other documents show that Washington County has a database of more than 300,000 mugshots that is indexed by Rekognition.
• The Orange County district is no longer looking to use a rate benchmark indexed by the Metropolitan Water District.
• Kudlow also said that the next phase should include a lower capital gains rate -- and a rate that’s indexed for inflation.

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.

## First Known Use of index

1720

in the meaning defined at transitive sense 1a

See Words from the same year
NEW! Time Traveler

## index Synonyms

###### Synonyms

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

###### Related Words

book, card, file, note;

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 of 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.

## Definition of index for English Language Learners

• : 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

1

## index

noun in·dex \ ˈin-ˌdeks \

## Definition of index for Students

plural indexes or indices \ˈin-də-ˌsēz\
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 1
• the index on a scale
3 : 1sign 3, indication
• Prices are an index of business conditions.

2

verb

## Definition of index for Students

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

## index

noun in·dex \ ˈin-ˌdeks \

## medical Definition of index

plural indexes or indices\-də-ˌsēz\
1
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
3 a : 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 juice
• Journal 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

1

noun in·dex

## legal Definition of index

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

2

transitive verb

## legal Definition of index

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

## Seen and Heard

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