Source : Webster's Revised Unabridged Dictionary (1913)

Whacker \Whack"er\, n.
   1. One who whacks. [Colloq.]

   2. Anything very large; specif., a great lie; a whapper.
      [Colloq.]

Source : WordNet®

whacker
     n : something especially big or impressive of its kind [syn: {whopper}]

Source : Free On-Line Dictionary of Computing

whacker
     
        [University of Maryland: from {hacker}] 1. A person, similar
        to a {hacker}, who enjoys exploring the details of
        programmable systems and how to stretch their capabilities.
        Whereas a hacker tends to produce great hacks, a whacker only
        ends up whacking the system or program in question.  Whackers
        are often quite egotistical and eager to claim {wizard}
        status, regardless of the views of their peers.  2. A person
        who is good at programming quickly, though rather poorly and
        ineptly.