1.
Abbr. ind. 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.
2. Something that reveals or indicates; a sign: "Her face . . . was a fair index to her disposition" (Samuel Butler).
3. Printing. A character (☞) used in printing to call attention to a particular paragraph or section. Also called fist, hand.
4. An indicator or a 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 on, an ordering relation involving, or a use of the associated expression. b. A number derived from a formula, used to characterize a set of data.
6. Index Roman Catholic Church. A list formerly published by Church authority, restricting or forbidding the reading of certain books.