Definition of "Index" :

noun: the finger next to the thumb

noun: an alphabetical listing of names and topics along with page numbers where they are discussed

noun: a number or ratio (a value on a scale of measurement) derived from a series of observed facts; can reveal relative changes as a function of time

noun: a mathematical notation indicating the number of times a quantity is multiplied by itself

noun: a numerical scale used to compare variables with one another or with some reference number

verb: adjust through indexation

"The government indexes wages and prices."

verb: provide with an index

"Index the book."

verb: list in an index