Source : Webster's Revised Unabridged Dictionary (1913)

Setback \Set"back`\, n.
   1. (Arch.) Offset, n., 4.

   2. A backset; a countercurrent; an eddy. [U. S.]

   3. A backset; a check; a repulse; a reverse; a relapse.
      [Colloq. U.S.]

Source : WordNet®

setback
     n : an unfortunate happening that hinders of impedes; something
         that is thwarting or frustrating [syn: {reverse}, {reversal},
          {blow}, {black eye}]