indexes

indexes — noun

1. the section at the end of a reference book where topics are listed from A to Z b

1.nounB1
Definition

the section at the end of a reference book where topics are listed from A to Z beside the pages where you can find them

Example

Sari checked the index at the back of the textbook for 'photosynthesis'.

look up a topic in the index

The index listed every character name and the pages where they appeared.

Common collocations
  • alphabetical index
  • comprehensive index
  • look something up in the index
  • check the index
  • build an index
  • a detailed index
Synonyms
  • catalogue

    a catalogue describes items in detail; an index only gives page locations

  • directory

    a directory lists people or organisations with contact details, not book pages

  • glossary

    a glossary defines terms; an index only shows where they appear

Usage Note

Distinguish from a table of contents, which lists chapters by order of appearance — an index lists topics alphabetically with page numbers.

Common Mistakes

I looked it up in the table of contents.
I looked it up in the index.
A table of contents lists chapters in order; an index lists topics alphabetically with page numbers.

2. an ordered set of entries kept in a digital database or on cards, sorted alphabe

2.nounB1
Definition

an ordered set of entries kept in a digital database or on cards, sorted alphabetically so each item can be found quickly

Example

The library's card index held records of every book acquired since 1920.

card index — a physical filing system

Hana typed a name into the database index and found the file instantly.

database index — a digital lookup structure

Common collocations
  • card index
  • database index
  • index cards
  • search the index
  • update an index
Synonyms
  • database

    a database stores full records; an index is a lookup structure within or alongside it

  • inventory

    an inventory lists all items owned; an index organises references to information

Usage Note

Most often encountered today in computing (database index, search engine index). The physical card-index system is now rare.

3. a number, often published regularly, that tracks how a group of related values c

3.nounB2
Definition

a number, often published regularly, that tracks how a group of related values changes over time compared to a starting point — for example, the consumer price index that measures living costs

Example

Tyler noticed the consumer price index had climbed and sighed at the rising cost of his weekly groceries.

consumer price index — a common economic index

Ishaan watches the stock market index every morning before making trades.

stock market index — tracks share prices

Common collocations
  • consumer price index
  • stock market index
  • index rises/falls
  • index of economic activity
  • housing price index
Synonyms
  • indicator

    broader term — any sign that shows something; an index is a specific calculated number

  • gauge

    often a physical measuring tool; an index is an abstract numerical scale

  • benchmark

    a fixed reference point for comparison, not necessarily tracking change over time

  • barometer

    suggests sensitivity to change; often used figuratively

Usage Note

Often appears in names of specific measures: consumer price index (CPI), retail price index (RPI), FTSE 100 index. The plural 'indexes' is more common than 'indices' in everyday economics writing.

4. a noticeable sign, number, or piece of evidence that reveals how strong, common,

4.nounB2
Definition

a noticeable sign, number, or piece of evidence that reveals how strong, common, or serious something is

Example

The number of empty shopfronts is a useful index of the town's decline.

an index of + [condition being measured]

Rising hospital admissions served as an index of how severe the flu season was.

Common collocations
  • a useful index of
  • a reliable index of
  • serve as an index of
  • a clear index of
Synonyms
  • sign

    more general and everyday; an index is more concrete and often quantifiable

  • indication

    a hint or signal; an index suggests a stronger, more reliable piece of evidence

Usage Note

This sense is more formal than everyday words like 'sign' or 'measure'. Often followed by 'of' to name what is being indicated.

5. short for index finger — the finger that sits beside the thumb and is normally u

5.nounB1
Definition

short for index finger — the finger that sits beside the thumb and is normally used when you point at something

Example

Noa wore a silver ring on her left index finger, just above the knuckle.

index finger — the full phrase

The doctor pressed his index finger gently against the patient's wrist.

Common collocations
  • index finger
  • left/right index finger
  • point with one's index finger
  • hold up an index finger
Synonyms
  • forefinger

    same meaning; 'index finger' is much more common in everyday speech

Usage Note

Almost always used in the phrase 'index finger.' Using 'index' alone to mean the finger is rare in everyday speech and sounds formal or old-fashioned.

Common Mistakes

I cut my first finger.
I cut my index finger.
English speakers almost never say 'first finger'; always use 'index finger.'

6. in mathematics, a small raised number or symbol written above and to the right o

6.nounC1
Definition

in mathematics, a small raised number or symbol written above and to the right of a base number that tells you how many times to multiply the base by itself

Example

Madison pointed at the tiny raised two on the board and said, 'That index tells us to square the five.'

that index tells us to — identifying what the index means

Cole wrote the index above the base number to show repeated multiplication.

Common collocations
  • index notation
  • raise the index
  • negative index
  • index of [number]
Synonyms
  • exponent

    same meaning; 'exponent' is more common in school-level maths

  • power

    related term — 'to the power of three' uses 'power,' not 'index'

Usage Note

This is a technical mathematics term. In school-level maths and everyday contexts, 'exponent' or 'power' is far more common than 'index.'

indexes — verb

Word family

  • index
    nounB1
  • index
    verbB2
  • indexation
    nounC1
  • indexer
    nounC2
  • indexical
    adjectiveC2

Synonym discussion

Sense: noun/3

These words all describe things that measure or show something, but they differ in precision and use. An indicator is the broadest — anything that points to a fact (rising sales are an indicator of growing demand). A gauge is often a physical measuring tool (a fuel gauge in a car) or a narrowly defined metric. An index is a calculated number that tracks change over time against a base value — the consumer price index, for instance, tracks inflation month by month. A benchmark is a fixed reference point for comparison (industry benchmarks for energy consumption), not something that moves with conditions. A barometer suggests sensitivity to change and is often figurative (consumer confidence is a barometer of economic health). Choose index for formal numerical tracking systems, indicator for looser evidence, gauge for specific instruments or metrics, benchmark for comparison targets, and barometer for vivid, change-sensitive measures.

indicator ↗gauge ↗benchmark ↗barometer ↗

Common collocations

Prepositions

Etymology

LatinEnglish

The word index comes from Latin index, meaning 'one who points out, a sign, a list, or the forefinger.' This Latin noun was formed from the verb indicare ('to point out, show, or declare'), which itself combines in- ('toward') and dicare ('to proclaim'). English borrowed the word directly from Latin in the late 14th century, first using it for the forefinger (because it is the pointing finger) and soon afterwards for the alphabetical list in a book (because it points readers to the right page). The mathematical and economic senses developed much later — the 'exponent' sense emerged in the 18th century, and the 'numerical comparison scale' sense became widespread in the 20th century with the rise of economic statistics.

First known use

1561

1561, in the meaning defined at sense 3a Verb