What is the meaning of index?

noun

• A numerical scale used to compare variables with one another or with some reference number.
• 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.
  • synonyms: index number, indicant, indicator
• A mathematical notation indicating the number of times a quantity is multiplied by itself.
  • synonyms: exponent, power
• An alphabetical listing of names and topics along with page numbers where they are discussed.
• The finger next to the thumb.
  • synonyms: index finger, forefinger

verb

• List in an index.
• Provide with an index.
  • usage: "index the book"
• Adjust through indexation.
  • usage: "The government indexes wages and prices"