index - definition and synonyms

noun [countable] 

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pluralindexes or indices
  1. 1
    an alphabetical list of something such as subjects or names at the back of a book, that shows on which page they are mentioned

    Look up the term you want in the index.

  2. 2
    economics a number that shows the price, value, or level of something compared with something else

    a wage/price index

    The Dow Jones index fell another 50 points yesterday.

  3. 3
    something that can be used for measuring how a situation is changing
    index of:

    The test provides parents with a reliable index of their child’s progress.

  4. 4
    maths a small number written or printed above and to the right of a number. It shows how many times the main number is to be multiplied by itself.