in·dex 
(ĭndĕks′)
(ĭndĕks′)n. pl. in·dex·es or in·di·ces (-dĭ-sēz′)
1. Something that serves to guide, point out, or otherwise facilitate reference, especially:
a. An alphabetized list of names, places, and subjects treated in a printed work, giving the page or pages on which each item is mentioned.
b. A thumb index.
c. A table, file, or catalog.
d. Computers A list of keywords associated with a record or document, used especially as an aid in searching for information.
2. Something that reveals or indicates; a sign: "Her face ... was a fair index to her disposition" (Samuel Butler).
3. A character (☞) used in printing to call attention to a particular paragraph or section. Also called hand.
4. An indicator or pointer, as on a scientific instrument.
5.
a. Mathematics A number or symbol, often written as a subscript or superscript to a mathematical expression, that indicates an operation to be performed, an ordering relation, or a use of the associated expression.
b. A number derived from a formula, used to characterize a set of data.
6.
a. A statistical value that represents the price or value of an aggregate of goods, services, wages, or other measurable quantities in comparison with a reference number for a previous period of time.
b. A number that represents the change in price or value of stocks or other securities in a particular market, sector, or asset class.
c. The stocks or other securities represented by an index.
7. Index Roman Catholic Church A list formerly published by Church authority, restricting or forbidding the reading of certain books.
tr.v. in·dexed, in·dex·ing, in·dex·es
1.
a. To furnish with an index: index a book.
b. To enter in an index.
2. To indicate or signal.
3. To adjust through indexation.
[Middle English, forefinger, from Latin; see deik- in the Appendix of Indo-European roots.]
index′er n.