noun (n)

• a person who pleads for a cause or propounds an idea(noun.person)

  Synonym:
  advocate, advocator, proponent
  

  source: wordnet30
• someone who expounds and interprets or explains(noun.person)

  source: wordnet30
• a mathematical notation indicating the number of times a quantity is multiplied by itself(noun.communication)

  Synonym:
  index, power
  

  source: wordnet30
• A number, letter, or any quantity written on the right hand of and above another quantity, and denoting how many times the latter is repeated as a factor to produce the power indicated(noun)

  source: webster1913