WordNet (r) 3.0 (2006):

shush
    v 1: silence (someone) by uttering `shush!'

Moby Thesaurus II by Grady Ward, 1.0:

82 Moby Thesaurus words for "shush":
   assibilate, assibilation, black out, buzz, censor, choke,
   choke off, dumbfound, effervesce, effervescence, effervescing,
   fizz, fizzle, fizzling, frication, frictional rustling, gag, hiss,
   hissing, hugger-mugger, hush, hush up, hush-hush, hushing, kill,
   lisp, muffle, muzzle, put to silence, quash, quiet, quieten,
   repress, rhonchus, shushing, shut down on, shut up, sibilance,
   sibilate, sibilation, siffle, sigmatism, silence, siss, sissing,
   sit on, sizz, sizzle, sizzling, smother, sneeze, sneezing, sniff,
   sniffle, snore, snort, snuff, snuffle, soft-pedal, spit, splutter,
   sputter, squash, squelch, squish, sternutation, stertor, stifle,
   still, strangle, strike dumb, suppress, swish, throttle, wheeze,
   whish, whistle, whistling, white noise, whiz, whoosh, zip