Source : Webster's Revised Unabridged Dictionary (1913)

Auditor \Au"di*tor\, n. [L. auditor, fr. audire. See {Audible},
   a.]
   1. A hearer or listener. --Macaulay.

   2. A person appointed and authorized to audit or examine an
      account or accounts, compare the charges with the
      vouchers, examine the parties and witnesses, allow or
      reject charges, and state the balance.

   3. One who hears judicially, as in an audience court.

   Note: In the United States government, and in the State
         governments, there are auditors of the treasury and of
         the public accounts. The name is also applied to
         persons employed to check the accounts of courts,
         corporations, companies, societies, and partnerships.

Source : WordNet®

auditor
     n 1: someone who listens attentively [syn: {hearer}, {listener},
          {attender}]
     2: a student who attends a course but does not take it for
        credit
     3: a qualified accountant who inspects the accounting records
        and practices of a business or other organization