Source : Webster's Revised Unabridged Dictionary (1913)

Equalizer \E"qual*iz`er\, n.
   1. = {Equalizing bar}.

   2. A device, as a bar, for operating two brakes, esp. a pair
      of hub brakes for an automobile, with equal force.

   3. (Elec.) Any device for equalizing the pull of
      electromagnets; also, a conductor of low resistance
      joining the armature ends of the series field coils of
      dynamos connected in parallel.

   4. (A["e]ronautics) A sliding panel to preserve the lateral
      stability of an a["e]roplane.

Equalizer \E"qual*i`zer\, n.
   One who, or that which, equalizes anything.

Source : WordNet®

equalizer
     n 1: electronic equipment that reduces frequency distortion [syn:
           {equaliser}]
     2: an equivalent counterbalancing weight [syn: {counterweight},
         {counterbalance}, {counterpoise}, {balance}, {equaliser}]
     3: a score that makes the match even