index
Verbindexes, indexing, indexed
Formsindexes, indexing, indexed
- 1An alphabetical listing of items along with the location where each one can be found.
Like a store directory that points you to the right aisle.
She scanned the index for any mention of the author's earlier works.
A well-made index lets readers locate a single fact in seconds.
UsagePlural indexes or indices; indexes is the usual one for books.
- 2A number expressing a property or ratio, such as a coefficient that measures some characteristic.
The refractive index of water is about 1.33.
Diamond has a very high refractive index, which helps it sparkle.
Similarcoefficient
Note
Science uses the word for a number that captures a property, often the ratio of two measured quantities. Refractive index is the classic case. Unlike the economist's price figure, it describes how one material behaves rather than summarizing a basket of values. Richard Feynman's The Feynman Lectures (1963) speaks of 'the indexes of the individual materials', so the plural indexes is at home in physics too.
Checked 31 Oct 2026 · 5 facts
- Refractive index expresses a material's optical property as a ratio. en.wikipedia.org
- An economic price index summarizes prices across a basket of goods and services. bls.gov
- Richard Feynman was an author of The Feynman Lectures on Physics. en.wikipedia.org
- The work began publication in 1963; the quoted passage is in Volume I. openlibrary.org
- The quoted wording occurs in the work, demonstrating the plural indexes in physics. feynmanlectures.caltech.edu
- 3A single figure calculated from a set of prices or quantities, used to track how they change overall.
Like a single grade that averages many test results into one number.
The consumer price index showed inflation slowing in the third quarter.
Economists revised the index after new wage data arrived.
UsageUsually a named figure: the consumer price index, a stock market index.
Note
Economics boils a whole basket of prices or quantities down to one figure. That figure is usually set to 100 at a chosen base period, so later values read as proportional change from that starting point. The consumer price index is the familiar example. Such a figure is what the verb for adjusting to inflation ties wages or benefits to.
Checked 31 Oct 2026 · 5 facts
- An economic index summarizes a set of prices or quantities in one figure. cy.ons.gov.uk
- An index is usually normalized to 100 for a chosen base period. bls.gov
- Subsequent index values express proportional change relative to the base period. ons.gov.uk
- The consumer price index is an example measuring changes in a basket of prices. bls.gov
- Wages and benefits can be linked to a price index to adjust for inflation. bls.gov
- 4To compile an alphabetical guide to the contents of a text, showing where each topic appears.
A professional was hired to index the dense legal volume.
She carefully indexed every name mentioned in the diaries.
Note
The verb has moved from the editor's desk into software. A database or search engine indexes text by recording where words occur, and some systems deliberately leave short and common words out.
Checked 2 Nov 2026 · 2 facts
- Software indexes text by recording associations between words and their locations in documents. postgresql.org
- Some indexing systems omit short words and common words. dev.mysql.com
- 5The forefinger; the finger beside the thumb, commonly used for pointing.
The surgeon flexed her index to test the nerve's response.
Guitar teachers often tell beginners to press the string with the tip of the index, not the flat pad.
UsageUsually index finger; the bare word is rare and can be unclear.
Similarforefinger, pointer
Note
The finger named for pointing: Latin index already meant the forefinger among other pointers and indicators, and the book's alphabetical list shares the same idea of showing the way.
- 6A data structure that speeds up operations on a database table, especially searches.
Creating an index on the email column sped up user lookups dramatically.
Every index consumes extra disk space and must be updated on each write.
Note
A database borrows the logic of a book's alphabetical list. Instead of reading every row, a query can consult an index structure, commonly a B-tree or hash, that helps locate the matching records. The speed has a price. Indexes take storage and may need updating when the table changes, so adding indexes can slow writes.
Checked 31 Oct 2026 · 7 facts
- A database index works by an analogy with a book's alphabetical index. postgresql.org
- An index can locate matching rows without examining every row. dev.mysql.com
- Secondary indexes commonly point to records, but clustered indexes can contain the row data themselves. dev.mysql.com
- B-tree and hash structures are established database index types. postgresql.org
- Indexes impose storage overhead. supabase.com
- Some changes require index maintenance, but others can avoid it. PostgreSQL's heap-only updates can leave ordinary indexes untouched. postgresql.org
- Additional indexes increase the maintenance cost of writes. dev.mysql.com
- 7An integer or key that marks the position of an item within an array, list, or similar data structure.
Like a locker number that points to one locker among many.
She accessed the element by passing its index to the function.
An out-of-range index threw an exception at runtime.
Similarsubscript
Note
Programmers name a position by its index. In zero-based schemes the first element carries index 0, so the tenth item sits at 9. An index can also be a key rather than a number, as in a hash table or associative array. Keep it apart from the database speed-up structure: this index is a position or key, while that one is a lookup aid.
Checked 31 Oct 2026 · 5 facts
- An index identifies an element's position in an array. docs.oracle.com
- In zero-based indexing, the first element has index 0 and the tenth has index 9. docs.oracle.com
- Associative arrays can be indexed by nonnumeric keys. docs.python.org
- An index identifies an element by position or key; it is not generally a memory address. An array element's address can be calculated from its index. en.wikipedia.org
- A database index aids lookup and can speed retrieval. postgresql.org
- 8A sign or indication that reveals the nature, existence, or degree of something.
Her trembling hands were an index of how nervous she felt.
The condition of a city's parks is an index of civic pride.
UsageUsed with of: trembling hands are an index of nerves.
Similarsign, indication, indicator, measure, gauge
Note
Here the pointing is done by evidence rather than by a finger: whatever reveals something hidden is its index, and the word takes of. John Arbuthnot's An Essay Concerning the Nature of Aliments (1731) calls tastes 'the Indexes of the different Qualities of Plants', treating the tongue as a reader of what lies inside a plant.
Checked 31 Oct 2026 · 3 facts
- John Arbuthnot wrote An Essay Concerning the Nature of Aliments. en.wikisource.org
- The book was first published in 1731, as confirmed by the first edition's title-page imprint. archive.org
- Arbuthnot calls tastes 'the Indexes of the different Qualities of Plants', using taste as evidence of plants' internal qualities. archive.org
Less common meanings
- 9To adjust a value for inflation by linking it to a price index, keeping its real level constant.
Lawmakers voted to index benefits so they track rising prices.
Their rent is indexed to inflation each January.
UsageUsed with to, mostly passive: pensions are indexed to inflation.
Note
What it protects is real value, the purchasing power of a sum, while the nominal figure is allowed to rise. The noun behind it is the economist's price figure. To index a payment is to let that figure steer it.
- 10To access a value in a data container by referring to its index.
Developers index the array with a loop variable to read each element.
The function indexes the dictionary by key to return the stored value.
Note
The working verb of the position number: to index an array or dictionary is to fetch the value stored at a given position or key. When data is stored side by side, any position can be reached directly, without stepping through the ones before it. Keep it apart from the verb for compiling an index, which builds a guide rather than reading a value.
Checked 31 Oct 2026 · 2 facts
- Arrays use positional indexes, while dictionaries retrieve values by keys. docs.python.org
- Contiguous array storage permits direct access without traversing preceding elements. docs.python.org
- 11To measure something by reference to an associated value.
Sociologists often index living standards by access to clean water.
The report indexes biodiversity by the number of species present.
UsageIndex one thing by another, or in the passive, be indexed to it.
Note
A figurative cousin of the inflation verb, met here in the passive with to. Samanth Subramanian, writing in 2019, says that 'human progress was indexed to the ease and speed of our mobility', with progress measured against walking, riding, sailing and flight. Unlike the inflation-adjusting verb, nothing is being corrected. One thing is simply read off another.
Checked 31 Oct 2026 · 2 facts
- Subramanian wrote the passage in 2019. theguardian.com
- The quotation is exact, and its surrounding sentence describes mobility through walking, riding animals, sailing and flight. en.wiktionary.org
- 12
- 13A small raised number showing the power to which a quantity is raised; an exponent.
In x⁴, the index 4 shows that four x's are multiplied together.
She forgot to lower the index when differentiating the term.
Note
The small raised 3 in x³ is its index, the figure that says how many times the base is multiplied by itself. Exponent names the same thing, and the two terms are interchangeable in this use. The raised position matters: a figure set below the line labels a quantity rather than raising it to a power.
Checked 31 Oct 2026 · 3 facts
- The raised 3 in x³ is an index, also called an exponent. en.wikipedia.org
- For x³, the exponent indicates how many times the base occurs as a factor. openstax.org
- A lowered number can identify a quantity, such as a member of a sequence, rather than indicate exponentiation. en.wikipedia.org
- 14To serve as an indexical sign for some situation or state of affairs; to indicate it.
In sociolinguistics, certain pronunciations index a speaker's regional background.
Dropping the g in 'running' can index a relaxed, casual tone.
Similarindicate, signal, mark, signify
Note
Linguists use the verb to say what a form signals about speaker, setting or identity. Haruko Minegishi Cook's Socializing Identities Through Speech Style (2008) writes that 'the feature I indexes the current speaker', and you the addressee. The signal works through its link to the speech situation, the logic of the noun for context-bound expressions.
Checked 2 Nov 2026 · 3 facts
- Haruko Minegishi Cook wrote Socializing Identities through Speech Style, published in 2008. linguistlist.org
- Cook's book contains the quoted wording and identifies you with the current addressee. en.wiktionary.org
- Indexical signs depend on their context of occurrence. en.wikipedia.org
- 15An introductory section or prologue that indicates what is to follow in a work.
Ay me, what act, that roars so loud and thunders in the index?
c. 1599, William Shakespeare, “The Tragedie of Hamlet, Prince of Denmarke”Note
An early modern use, now obsolete: the opening argument or prologue that announced what a work would contain. In Shakespeare's Hamlet the line 'what act, that roars so loud and thunders in the index?' means the deed sounds terrible from its preface alone. Modern readers expect the alphabetical list at a book's end, so the line is easily misread.
Checked 31 Oct 2026 · 3 facts
- Index had an early modern sense, now obsolete, meaning a prologue indicating what follows. en.wiktionary.org
- The quoted words occur in Shakespeare's Hamlet; the speaker is the Queen, Gertrude. folger.edu
- The line describes a deed that sounds terrible from its introductory description. en.wiktionary.org
- 16To use a mechanism to move an object step by step to a precise location.
- 17To make an inventory of something; to take stock of what is on hand.
- 18A typographic mark shaped like a hand with an extended finger, used to direct a reader's attention to a particular note or passage.
- 19In group theory, the number of distinct cosets of a subgroup within a group.
- 20An expression whose referent changes according to the context of use; 'today's newspaper,' for instance, points to a different paper each day.
Showing meanings only.
Practice
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Origin
From the Latin index ("a discoverer, informer, indicator, forefinger, or title"), formed from in- and dīcō ("to say, indicate"); related to indicō ("to point out, show") and to indicate.
Checked 31 Oct 2026 · 4 facts
- English index comes from Latin index. en.wiktionary.org
- Latin index means discoverer, informer, indicator, forefinger, or title. en.wiktionary.org
- Latin indicō means to point out or show. en.wiktionary.org
- Index is etymologically related to indicate. en.wiktionary.org