Source : Webster's Revised Unabridged Dictionary (1913)

Reliever \Re*liev"er\ (-?r), n.
   One who, or that which, relieves.

Source : WordNet®

reliever
     n 1: someone who takes the place of another (as when things get
          dangerous or difficult); "the star had a stand-in for
          dangerous scenes"; "we need extra employees for summer
          fill-ins" [syn: {stand-in}, {substitute}, {relief}, {backup},
           {backup man}, {fill-in}]
     2: a person who reduces the intensity (e.g., of fears) and
        calms and pacifies; "a reliever of anxiety"; "an allayer
        of fears" [syn: {allayer}, {comforter}]
     3: a pitcher who does not start the game [syn: {relief pitcher},
         {fireman}]