WordNet (r) 3.0 (2006):

escalate
    v 1: increase in extent or intensity; "The Allies escalated the
         bombing" [syn: escalate, intensify, step up] [ant:
         de-escalate, step down, weaken]

Moby Thesaurus II by Grady Ward, 1.0:

54 Moby Thesaurus words for "escalate":
   boost, broaden, buoy up, cast up, climb, elevate, enlarge, erect,
   escalade, expand, grow, heave, heft, heighten, heist, hike, hoick,
   hoist, hold up, increase, intensify, jerk up, knock up, levitate,
   lift, lift up, lob, loft, mount, perk up, raise, raise up, rear,
   rear up, rise, scale, set up, sky, spread, stick up, throw up, up,
   upbuoy, upcast, upclimb, upgo, upheave, uphoist, uphold, uplift,
   upraise, uprear, upthrow, widen