Definitions 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 numerical scale used to compare variables with one another or with some reference number
• noun:   a mathematical notation indicating the number of times a quantity is multiplied by itself
• verb:   provide with an index

  Example: "Index the book"

• verb:   list in an index
• verb:   adjust through indexation

  Example: "The government indexes wages and prices"