Source : Webster's Revised Unabridged Dictionary (1913)

Step-down \Step"-down`\, a. (Elec.)
   Transforming or converting a current of high potential or
   pressure into one of low pressure; as, a step-down
   transformer.

Source : WordNet®

step-down
     n : the act of decreasing or reducing something [syn: {decrease},
          {diminution}, {reduction}] [ant: {increase}]