WordNet (r) 3.0 (2006):

shut up
    adj 1: closely confined [syn: pent, shut up(p)]
    v 1: refuse to talk or stop talking; fall silent; "The children
         shut up when their father approached" [syn: close up,
         clam up, dummy up, shut up, belt up, button up,
         be quiet, keep mum] [ant: open up]
    2: place in a place where something cannot be removed or someone
       cannot escape; "The parents locked her daughter up for the
       weekend"; "She locked her jewels in the safe" [syn: lock
       in, lock away, lock, put away, shut up, shut away,
       lock up]
    3: cause to be quiet or not talk; "Please silence the children
       in the church!" [syn: hush, quieten, silence, still,
       shut up, hush up] [ant: louden]

Moby Thesaurus II by Grady Ward, 1.0:

177 Moby Thesaurus words for "shut up":
   anchoritic, answer, answer conclusively, argue down, bang, bar,
   barricade, batten, batten down, be mute, be silent, beleaguer,
   beset, besiege, blockade, bolt, bottle up, bound, box in, box up,
   button, button up, cage, cease, chamber, check, choke, choke off,
   clap, cloister, cloistered, close, close down, close in,
   close shop, close up, compass, confine, confound, confute,
   constrain, constrict, contain, contract, contradict, controvert,
   coop, coop in, coop up, cordon, cordon off, cork up, corral, cover,
   crib, crush, defeat, demolish, deny, detain, dismiss, dispose of,
   domestic, dry up, dummy up, encage, encircle, enclose, encompass,
   enshrine, eremitic, fasten, fence in, finish, floor, fold, fold up,
   forswear speech, hedge in, hem in, hermitic, hermitish, hold,
   hold in custody, hold in restraint, house in, hush, immure,
   impound, imprison, incarcerate, include, inhibit, jail, keep in,
   keep in custody, keep in detention, keep mum, keep quiet,
   keep silent, keep still, kennel, key, latch, leaguer, lock,
   lock out, lock up, make no sign, mew, mew up, nonplus, occlude,
   overthrow, overturn, overwhelm, padlock, parry, pen, pen in,
   pen up, pipe down, play dumb, plumb, pocket, pound, put to silence,
   quarantine, quiet, quiet down, quieten, rail in, rebut, recluse,
   reduce to silence, refute, restrain, restrict, say nothing, seal,
   seal off, seal up, secure, sequestered, settle, shackle, shrine,
   shush, shut, shut down, shut in, shut the door, shut up shop,
   shutter, silence, slam, smash all opposition, snap, soft-pedal,
   squash, squeeze shut, squelch, stable, stand mute, stay-at-home,
   still, strangle, subvert, surround, undermine, upset, wall in,
   wrap, yard, yard up, zip up, zipper