Source : Webster's Revised Unabridged Dictionary (1913)

Rack \Rack\, v. t.
   1. To extend by the application of force; to stretch or
      strain; specifically, to stretch on the rack or wheel; to
      torture by an engine which strains the limbs and pulls the
      joints.

            He was racked and miserably tormented. --Pope.

   2. To torment; to torture; to affect with extreme pain or
      anguish.

            Vaunting aloud but racked with deep despair.
                                                  --Milton.

   3. To stretch or strain, in a figurative sense; hence, to
      harass, or oppress by extortion.

            The landlords there shamefully rack their tenants.
                                                  --Spenser.

            They [landlords] rack a Scripture simile beyond the
            true intent thereof.                  --Fuller.

            Try what my credit can in Venice do; That shall be
            racked even to the uttermost.         --Shak.

   4. (Mining) To wash on a rack, as metals or ore.

   5. (Naut.) To bind together, as two ropes, with cross turns
      of yarn, marline, etc.

   {To rack one's brains} or {wits}, to exert them to the utmost
      for the purpose of accomplishing something.

   Syn: To torture; torment; rend; tear.

Source : WordNet®

wits
     n : the basic human power of intelligent thought and perception;
         "he used his wits to get ahead"; "I was scared out of my
         wits"; "he still had all his marbles and was in full
         possession of a lively mind" [syn: {marbles}]