WordNet (r) 3.0 (2006):

step up
    v 1: increase in extent or intensity; "The Allies escalated the
         bombing" [syn: escalate, intensify, step up] [ant:
         de-escalate, step down, weaken]
    2: speed up; "let's rev up production" [syn: rev up, step
       up]
    3: make oneself visible; take action; "Young people should step
       to the fore and help their peers" [syn: come to the fore,
       step forward, come forward, step up, step to the
       fore, come out]

Moby Thesaurus II by Grady Ward, 1.0:

119 Moby Thesaurus words for "step up":
   accelerando, accelerate, acceleration, accost, advance, aggravate,
   aggravation, amplify, approach, appropinquate, approximate,
   bear down on, bear down upon, bear up, beef up, beefing-up,
   blow up, blowing up, blowup, charge, close, close in, close with,
   come, come closer, come forward, come near, come on, come up,
   complicate, concentrate, concentration, condensation, condense,
   confront, consolidate, consolidation, crack on, deepen, deepening,
   double, draw near, draw nigh, drive, electrify, encounter,
   energize, enhance, enhancement, exacerbate, exacerbation,
   exaggerate, exaggeration, explosion, gain ground, gain upon,
   galvanize, generate, getaway, hasten, heat up, heating-up,
   heighten, heightening, hop up, hot up, hurry, hurry up, impetus,
   information explosion, intensification, intensify, jazz up, key up,
   loop in, magnification, magnify, make complex, narrow the gap,
   near, open the throttle, pick up speed, pickup, plug in,
   population explosion, proximate, put on, put on steam, quicken,
   quickening, race, ramify, redouble, redoubling, reinforce,
   reinforcement, rev, shake up, sharpen, shock, short, short-circuit,
   sidle up to, soup up, speed up, speedup, step down, step on it,
   stiffen, strengthen, strengthening, switch off, switch on, thrust,
   tightening, triple, turn off, turn on, whet