The Collaborative International Dictionary of English v.0.48:

Step-up \Step"-up`\, a. (Elec.)
   Transforming or converting a low-voltage current into one of
   high voltage; as, a step-up transformer.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

step-up
    n 1: the act of increasing something; "he gave me an increase in
         salary" [syn: increase, step-up] [ant: decrease,
         diminution, reduction, step-down]