WordNet (r) 3.0 (2006):

keep down
    v 1: place a limit on the number of [syn: number, keep down]
    2: put down by force or intimidation; "The government quashes
       any attempt of an uprising"; "China keeps down her dissidents
       very efficiently"; "The rich landowners subjugated the
       peasants working the land" [syn: repress, quash, keep
       down, subdue, subjugate, reduce]
    3: manage not to throw up [ant: barf, be sick, cast,
       cat, chuck, disgorge, honk, puke, purge,
       regorge, regurgitate, retch, sick, spew, spue,
       throw up, upchuck, vomit, vomit up]

Moby Thesaurus II by Grady Ward, 1.0:

96 Moby Thesaurus words for "keep down":
   asphyxiate, beat down, bottle up, break, browbeat, bulldoze, bully,
   castrate, censor, choke off, clamp down on, coerce, compel, cork,
   cork up, cow, crack down on, crush, damp down, daunt,
   deprive of freedom, despotize, disenfranchise, disfranchise,
   dominate, domineer, domineer over, drown, enslave, enthrall,
   extinguish, gag, grind, grind down, henpeck, hold captive,
   hold down, hold in bondage, hold in captivity, hold in leash,
   hold in subjection, intimidate, jump on, keep under, kill,
   lead captive, lord it over, make dependent, muzzle, oppress,
   overawe, overbear, overmaster, override, peonize, pour water on,
   press heavy on, put down, quash, quell, quench, repress, ride over,
   ride roughshod over, shut down on, silence, sit down on, sit on,
   smash, smother, squash, squelch, stanch, stifle, strangle,
   stultify, subdue, subject, subjugate, subordinate, suffocate,
   suppress, take captive, terrorize, throttle, trample down,
   trample upon, tread down, tread upon, tyrannize, tyrannize over,
   unman, vassalize, walk all over, walk over, weigh heavy on