WordNet (r) 3.0 (2006):

bear down
    v 1: exert a force with a heavy weight; "The snow bore down on
         the roof" [syn: drag down, bear down, bear down on,
         press down on, weigh down]
    2: contract the abdominal muscles during childbirth to ease
       delivery [syn: bear down, overbear]
    3: to make a rush at or sudden attack upon, as in battle; "he
       saw Jess charging at him with a pitchfork" [syn: charge,
       bear down]
    4: exert full strength; "The pitcher bore down"
    5: pay special attention to; "The lectures bore down on the
       political background"
    6: exert a force or cause a strain upon; "This tax bears down on
       the lower middle class"

Moby Thesaurus II by Grady Ward, 1.0:

57 Moby Thesaurus words for "bear down":
   beat down, bring low, buckle down, couch, crush, debase, defeat,
   depress, detrude, do double duty, downbear, elucubrate, endeavor,
   get cracking, get cutting, go all out, haul down, hit the ball,
   hop to it, hotfoot, hump, hump it, hustle, indent, knuckle down,
   lay to, lean on it, let down, lower, lucubrate, overpower,
   overwork, ply the oar, pour it on, press down, pull down,
   push down, reduce, scratch, shag ass, shake a leg, shake it up,
   sink, slave, snap to it, spare no effort, step on it, subdue,
   subjugate, sweat, take down, tear ass, thrust down, vanquish,
   work hard, work late, work overtime