index

Etymology

From Latin index (“a discoverer, informer, spy; of things, an indicator, the forefinger, a title, superscription”), from indicō (“point out, show”); see indicate.

noun

1. An alphabetical listing of items and their location.
   The index of a book lists words or expressions and the pages of the book upon which they are to be found.
2. The index finger; the forefinger.
3. A movable finger on a gauge, scale, etc.
4. (typography) A symbol resembling a pointing hand, used to direct particular attention to a note or paragraph.
5. That which points out; that which shows, indicates, manifests, or discloses.
6. A sign; an indication; a token.
   His son's empty guffaws […] struck him with pain as the indices of a weak mind. 1887, Robert Louis Stevenson, The Misadventures of John Nicholson
7. (linguistics) A type of noun where the meaning of the form changes with respect to the context; e.g., 'Today's newspaper' is an indexical form since its referent will differ depending on the context. See also icon and symbol.
8. (economics) A single number calculated from an array of prices or of quantities.
9. (sciences) A number representing a property or ratio; a coefficient.
   In other words, we predict that the index for a new pair of materials can be obtained from the indexes of the individual materials, both against air or against vacuum. 1963, Richard Feynman, “Chapter 26, Optics: The Principle of Least Time”, in The Feynman Lectures on Physics, volume I
10. (mathematics) A raised suffix indicating a power.
11. (computing, especially programming and databases) An integer or other key indicating the location of data, e.g. within an array, vector, database table, associative array, or hash table.
12. (computing, databases) A data structure that improves the performance of operations on a table.
13. (obsolete) A prologue indicating what follows.

verb

1. (transitive) To arrange an index for something, especially a long text.
   MySQL does not index short words and common words.
2. To inventory; to take stock.
3. (chiefly economics) To normalise in order to account for inflation; to correct for inflation by linking to a price index in order to maintain real levels.
4. To measure by an associated value.
   For thousands of years, human progress was indexed to the ease and speed of our mobility: our capacity to walk on two legs, and then to ride on animals, sail on boats, chug across the land and fly through the air, all to procure for ourselves the food and materials we wanted. November 21 2019, Samanth Subramanian, “How our home delivery habit reshaped the world”, in The Guardian
5. (linguistics, transitive) To be indexical for (some situation or state of affairs); to indicate.
   For example, the feature I indexes the current speaker in the speech event and you, the current addressee. 2008, Haruko Minegishi Cook, Socializing Identities Through Speech Style, page 22
6. (computing) To access a value in a data container by an index.