index

index — noun

IPA/ˈɪndeks/
KK[ˈɪndɛks]IPA/ˈɪndeks/
  • indexsingular
  • indexesplural

1. An ordered list, usually arranged alphabetically, of the important names, subjec

1.nounB2
Definition

An ordered list, usually arranged alphabetically, of the important names, subjects, and topics appearing in a book or document, together with the page numbers where each item can be found.

Example

After finishing her novel, Amara created a detailed index of characters and places for her readers.

collocation: create an index

Wei checked the index at the back of the history book to find the page about the Tang dynasty.

Common collocations
  • compile an index
  • consult the index
  • appear in the index
  • index entry
  • index page
Synonyms
  • concordance

    a more detailed alphabetical list of every important word in a text, used especially for analysing literature or scripture

  • glossary

    a list of specialised terms with definitions, not page numbers

Common Mistakes

I found the information from the index of contents.
I found the information in the index.
'table of contents' is at the front of a book; 'index' is at the back and lists specific topics alphabetically.

2. A number or system that tracks how the value, level, or performance of something

2.nounB2
Definition

A number or system that tracks how the value, level, or performance of something changes over time, such as stock prices, the cost of living, or economic output.

Example

The consumer price index rose by three percent last year, making food and housing noticeably more expensive.

collocation: consumer price index / stock market index

Nadia compared the economic index of three Southeast Asian countries to see which one grew the fastest.

Common collocations
  • economic index
  • price index
  • index rose / fell
  • index of consumer confidence
  • track an index
Synonyms
  • indicator

    a broader term for any sign or signal of a condition; less precise than index

  • benchmark

    a fixed reference point used for comparison, not necessarily a composite number

  • gauge

    an informal measure, often approximate rather than exact

Usage Note

Often appears in compound nouns such as 'consumer price index', 'stock market index', or 'body mass index'. The preposition 'of' follows when specifying what is being measured.

3. A small figure or mark positioned above and to the right of a base number, indic

3.nounC1
Definition

A small figure or mark positioned above and to the right of a base number, indicating how many times that base should be multiplied by itself.

Example

In the expression 2⁵ = 32, the small five above the two is called the index.

technical term: index = exponent in mathematics

The maths teacher showed the class how to add the indices when multiplying powers of the same base.

Common collocations
  • raised to the index of
  • add / multiply indices
  • index of a power
Synonyms
  • exponent

    the more common term in modern mathematics for this concept

  • power

    refers to the whole operation (the base raised to the exponent)

Usage Note

In British English the plural is often 'indices' rather than 'indexes'. Common in algebra and scientific notation. The terms 'index' and 'exponent' are interchangeable in this sense.

Common Mistakes

The index is the large number at the bottom.
The index is the small number written at the top right.
the index is the superscript, not the base.

4. The long, slender finger located beside the thumb, commonly used for pointing at

4.nounA2
Definition

The long, slender finger located beside the thumb, commonly used for pointing at things or pressing small controls.

Example

Keiko pointed at the menu with her index finger to show the waiter which dish she wanted.

body part: index finger = the pointing finger

Guo accidentally hit his index finger with a hammer while fixing the wooden shelf in the garage.

Common collocations
  • index finger of the right / left hand
  • use one's index finger
  • point with one's index finger
Synonyms

index — verb

IPA/ˈɪn.deks/
KK[ˈɪndɛks]IPA/ˈɪn.deks/

Word family

  • indexation
    nounC1
  • indexer
    nounC1
  • indexical
    adjectiveC2

Synonym discussion

Sense: noun/2

Index, indicator, benchmark, and gauge all relate to measuring or tracking something, but they differ in precision and scope. An index is a composite numerical measure derived from multiple data points — for example, the consumer price index tracks a basket of goods and services to show changes in living costs. An indicator is a broader term for any sign or signal that reveals a trend or condition, such as 'rising unemployment is a key economic indicator.' A benchmark is a standard or reference point used for comparison, like 'the S&P 500 serves as a benchmark for US stock fund performance.' A gauge is a more informal word for an approximate measure, such as 'test scores are a rough gauge of student progress.' When choosing between these words, use index for official composite figures, indicator for general signs of a trend, benchmark when comparing against a standard, and gauge for rough estimates.

index ↗indicator ↗benchmark ↗gauge ↗

Common collocations

Nouns

Adverbs

Phrases

  • compile an index
  • consult the index
  • create an index
  • search the index
  • be indexed to
  • index-linked

Prepositions

  • in an index
  • by an index
  • to an index
  • indexed to

Etymology

LatinEnglish

From Latin 'index' meaning 'one who points out, informer, or pointer,' derived from 'indicāre' — 'to point out or show' (formed from 'in-' meaning toward, and 'dicāre' meaning to proclaim). The 'alphabetical list of contents' meaning first appeared in the late 1500s, while the 'finger that points' sense dates from the 1700s. The mathematical meaning (exponent) emerged around the same period. The verb sense 'to provide with an index' appeared in the early 1800s, and 'to adjust by index' developed in the 20th century with the growth of economic policy.