The Collaborative International Dictionary of English v.0.48:

equaliser \equaliser\ n.
   1. (Electronics) an electronic circuit which reduces
      frequency distortion.

   Syn: equalizer.
        [WordNet 1.5]

   2. an equivalent counterbalancing weight.

   Syn: counterweight, counterbalance, counterpoise, balance,
        equalizer.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

equaliser
    n 1: electronic equipment that reduces frequency distortion
         [syn: equalizer, equaliser]
    2: a weight that balances another weight [syn: counterweight,
       counterbalance, counterpoise, balance, equalizer,
       equaliser]