Source : Webster's Revised Unabridged Dictionary (1913)

Operator \Op"er*a`tor\, n. [L.]
   1. One who, or that which, operates or produces an effect.

   2. (Surg.) One who performs some act upon the human body by
      means of the hand, or with instruments.

   3. A dealer in stocks or any commodity for speculative
      purposes; a speculator. [Brokers' Cant]

   4. (Math.) The symbol that expresses the operation to be
      performed; -- called also {facient}.

Source : WordNet®

operator
     n 1: (mathematics) a symbol that represents a function from
          functions to functions; "the integral operator"
     2: an agent that operates some apparatus or machine; "the
        operator of the switchboard" [syn: {manipulator}]
     3: someone who owns or operates a business; "who is the
        operator of this franchise?"
     4: a shrewd or unscrupulous person who knows how to circumvent
        difficulties [syn: {hustler}, {wheeler dealer}]
     5: a speculator who trades aggressively on stock or commodity
        markets

Source : Free On-Line Dictionary of Computing

operator
     
         A symbol used as a {function}, with {infix
        syntax} if it has two arguments (e.g. "+") or {prefix syntax} if
        it has only one (e.g. {Boolean} NOT).  Many languages use
        operators for built-in functions such as arithmetic and logic.
     
        (1995-04-30)