Definition of index

Short definition: The word index means an organized list, usually found at the back of a book or on a website, that helps you quickly find specific topics, names, or information by pointing to where they appear.

Looking for a clear and natural explanation of the word index? The word index is widely used in books, technology, business, and everyday life to describe a guide, list, or sign that helps people find information more easily. You can see an index at the back of a book, in a database, in search engines, and even in economics. Because of this, index is a practical word that connects organization with understanding. Below, each meaning is explained in a natural and human way, so it feels simple and useful in real situations.

Forms: index, indexes, indices
Related: indicate v., indicator n.
Syllable: in-dex

1. A list that helps you find information quickly.

   An index is a list, usually found at the back of a book, that shows important topics and where to find them. Instead of searching page by page, people use the index to go straight to what they need.

   She checked the index to find the chapter on history.
   The book’s index made research much easier.
   He looked up the word in the index.

   Synonyms: guide list, reference list, topic list, content guide, lookup list, page guide, reference tool, finding aid, navigation list, subject list, search guide, book guide
   Antonyms: random pages, unsorted content, messy layout, unorganized text, no guide, confusing structure, scattered information, unordered list, chaotic format, unclear system, disorganized content, no reference

2. A number that shows change or performance.

   In business and economics, an index is a number that shows how something changes over time. Stock market indexes, for example, show whether the market is rising or falling. This helps people understand trends instead of single events.

   The stock index rose sharply today.
   Investors watch the index to track the market.
   The economic index shows signs of recovery.

   Synonyms: indicator number, market measure, performance scale, trend marker, financial barometer, progress measure, data indicator, economic signal, rating scale, change meter, growth indicator, benchmark number
   Antonyms: guess, random number, unclear sign, no measurement, uncertainty, vague signal, untracked change, unmeasured trend, blind estimate, unrecorded data, unclear result, no indicator

3. A sign that shows something is happening.

   More generally, an index can mean any sign or signal that points to a condition or situation. A high crime index, for example, suggests that safety is a concern. In this sense, index means evidence.

   His smile was an index of his happiness.
   Pollution levels are an index of environmental health.
   Her silence was an index of her anger.

   Synonyms: sign, signal, clue, indicator, evidence, marker, hint, symptom, measure, pointer, guide sign, telling sign
   Antonyms: mystery, unclear signal, hidden sign, no clue, uncertainty, silence without meaning, unknown factor, invisible sign, no evidence, confusion, unclear message, lack of signal

4. A system for organizing data in technology.

   In computers and databases, an index is a tool that makes searching faster. It organizes data so information can be found quickly, just like the index in a book, but in digital form.

   The database uses an index to speed up searches.
   Adding an index improved system performance.
   The search engine builds a large index of websites.

   Synonyms: data organizer, search tool, lookup system, digital guide, retrieval structure, access map, database helper, info locator, search framework, file guide, data map, system guide
   Antonyms: slow search, unorganized data, random storage, messy database, no structure, manual search, chaotic system, disordered files, unsorted data, no access guide, inefficient system, data confusion

5. A word that means pointing or directing attention.

   As a verb idea in meaning, index can suggest pointing toward something. It shows where attention should go, whether in books, data, or ideas. This meaning connects index with guidance and direction.

   The chart indexes the most important changes.
   His comments indexed a growing problem.
   The report indexes the key issues clearly.

   Synonyms: point to, indicate, highlight, mark, direct attention, signal, guide, show, underline, emphasize, refer to, point out
   Antonyms: ignore, hide, overlook, miss, conceal, downplay, distract, mislead, cover up, blur, obscure, misdirect