Home / Words /

Plural of “Index” (Grammar + Examples)

What is the plural of the word “index?” The pluralization of nouns follows distinct grammar rules in the English language. Some require a change in spelling (or a change in the affix). While others merely need a “-S” or “-ES” at the end of the base form.

The word “index” is a term that follows both grammar pluralization rules. Meaning the word “index” has more than one plural form. This causes many people frustration when learning English and choosing the proper word form.

Plural of index
Plural of index

What is the Plural Form of the Word “Index?”

The singular form of the word “index” has two plural forms. The plural of the word index is indexes and indices.

“Index” can be used as a noun and verb. In mathematics, the word “indices” are the plural form of the base word “index.” It’s important to remember that the plural word “indices” is derived from the Latin root form.

The noun index utilizes the -ES affix to indicate the plural and possessive form when it refers to a directory, as is customary in English.

When referring to several indexes, “indices” and “indexes” are both acceptable plural versions of the word “index.”

This makes the word “index” an uncommon English word with two distinct plural forms.

While “indexes” adopted the English form of pluralization by adding a -S or -ES, the word “indices” is a Latin multiple (meaning already pluralized). Although both share the same meaning (with the technical plural form being indexes versus indices).

In mathematical, scientific, and statistical contexts, the term “indices” is correct to use. It is used to refer to numbers, symbols, and figures to compare a value to a standard.

Typically, “indexes” refers to written materials like bibliographical or citation listings. When exchanges or financial news sites discuss multiple indices, the terms “indices” and “indices” are commonly used interchangeably. However, “indices” is more frequently used when discussing stocks.

Plural of index
Plural of index

When to Use Indices

The word “index” refers to a system in the plural noun form of “indices,” one of the plural versions of “index.” This refers to systems that track changes and compare values. Most commonly used in the context of finance. Only in this context (finance) are “indices” and “indexes” correctly interchangeable.

Examples of Using Indices in a Sentence:

  • Simple indices measure several characteristics of the British Isles’ synoptic climatology.
  • However, given that the percentage and absolute indices of unsteadiness have increased recently, further discussion of the issue is not necessary now.
  • The mean index of refraction is approximately me, and there aren’t many high indices.
  • The refractive indices for various wavelengths must be known for each type of glass used.
  • An Observed Fauna is provided by the biological sample collected at the test location, and biotic indices are also computed using this data.
  • Instead of using bezel inserts, which might corrode or come loose at great depths, the indices are machined directly onto the bezel.
  • These indices frequently examine patients using albumin and immunological state indicators such as total lymphocyte count.
  • This website also allows you to contrast the Libor rate with other well-known indices.

When to Use Indexes

Unlike “indices,” which are restricted to finance, “indexes” is the plural form of the word “index.” And has a far more comprehensive range of meanings. First, “indexes” can be used as a noun to refer to alphabetical lists of topics, names, titles, etc.

These lists are typically located on a book’s first page and indicate pages where each chapter can be found. Second, it can also describe a group of data organized alphabetically and kept on a computer (like a database).

However, “indexes” can also get used as a noun to refer to other things (like index fingers). For example, “The indexes of his fingers were sore.”

Examples of Using Indexes in a Sentence:

  • He conducted his analysis under the presumption that no indexes were created for malicious intent.
  • Death Indexes – This is a thorough index of county-organized links to historical societies, cemeteries, and obituaries.
  • Online access to the Bureau of Vital Statistics’ divorce indexes is free.
  • Public record indexes and photos can be found on numerous websites run by federal, state, and local governments.
  • Your local library has many marriage and death indexes on microfilm.
  • The Project Office offers the indexes to the usage statistics pages.
  • The Society started buying microfilm of the GRO indexes a few years ago.
  • Only decrees that have been sent to the Bureau are eligible for indexes.
  • These indexes provide details on state-wide divorces and annulments.
  • Additionally, you can create your indexes by combining hashing and B-tree methods.
  • The county-organized indexes are available on microfilm.


When is index used in technical contexts?

Typically, when referring to a database. An index of a database isn’t too dissimilar to the index of a book.

Which is used more “indexes” or “indices?”

“Indexes” is the more modern American usage of the word.


Fact checked:
Content is rigorously reviewed by a team of qualified and experienced fact checkers. Fact checkers review articles for factual accuracy, relevance, and timeliness. Learn more.

About the author

Dalia Y.: Dalia is an English Major and linguistics expert with an additional degree in Psychology. Dalia has featured articles on Forbes, Inc, Fast Company, Grammarly, and many more. She covers English, ESL, and all things grammar on GrammarBrain.

Thank you! Your submission has been received!
Oops! Something went wrong while submitting the form.