Source : Webster's Revised Unabridged Dictionary (1913)

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

Source : WordNet®

step-up
     n : the act of increasing something; "he gave me an increase in
         salary" [syn: {increase}] [ant: {decrease}]