[1] : The Collaborative International Dictionary of English v.0.48

step-down \step"-down`\, a. elec.
   transforming or converting a current of high potential or
   voltage into one of low voltage; as, a step-down transformer.
   webster 1913 suppl.

[2] : WordNet (r) 2.0

step-down
     n : the act of decreasing or reducing something syn: decrease,
          diminution, reduction ant: increase
see also:
decrease diminution reduction increase 

Step-Down >> S Words
Step-Down, definition of term: Step-Down
step-down_pag1.html