The Collaborative International Dictionary of English v.0.48:

Hush \Hush\, n.
   Stillness; silence; quiet. [R.] "It is the hush of night."
   --Byron.
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   Hush money, money paid to secure silence, or to prevent the
      disclosure of facts. --Swift.
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The Collaborative International Dictionary of English v.0.48:

Hush \Hush\, a.
   Silent; quiet. "Hush as death." --Shak.
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The Collaborative International Dictionary of English v.0.48:

Hush \Hush\ (h[u^]sh), v. t. [imp. & p. p. Hushed (h[u^]sht);
   p. pr. & vb. n. Hushing.] [OE. huschen, hussen, prob. of
   imitative origin; cf. LG. hussen to lull to sleep, G. husch
   quick, make haste, be silent.]
   1. To still; to silence; to calm; to make quiet; to repress
      the noise or clamor of.
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            My tongue shall hush again this storm of war.
                                                  --Shak.
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   2. To appease; to allay; to calm; to soothe.
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            With thou, then,
            Hush my cares?                        --Otway.
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            And hush'd my deepest grief of all.   --Tennyson.
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   To hush up, to procure silence concerning; to suppress; to
      keep secret. "This matter is hushed up." --Pope.
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The Collaborative International Dictionary of English v.0.48:

Hush \Hush\, v. i.
   To become or to keep still or quiet; to become silent; --
   esp. used in the imperative, as an exclamation; be still; be
   silent or quiet; make no noise.
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         Hush, idle words, and thoughts of ill.   --Keble.
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         But all these strangers' presence every one did hush.
                                                  --Spenser.
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WordNet (r) 3.0 (2006):

hush
    n 1: (poetic) tranquil silence; "the still of the night" [syn:
         hush, stillness, still]
    v 1: become quiet or still; fall silent; "hush my baby!"
    2: 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]
    3: become quiet or quieter; "The audience fell silent when the
       speaker entered" [syn: quieten, hush, quiet, quiesce,
       quiet down, pipe down] [ant: louden]
    4: wash by removing particles; "Wash ores"
    5: run water over the ground to erode (soil), revealing the
       underlying strata and valuable minerals

Moby Thesaurus II by Grady Ward, 1.0:

152 Moby Thesaurus words for "hush":
   allay, appease, assibilate, assibilation, awful silence, black out,
   buzz, calm, calm down, censor, choke, choke off, compose, conceal,
   cool, cover up, cradle, dead, dead of night, deathlike silence,
   dulcify, dumbfound, ease, effervesce, effervescence, effervescing,
   even out, fall silent, fizz, fizzle, fizzling, frication,
   frictional rustling, gag, gentle, golden silence, hide, hiss,
   hissing, hugger-mugger, hugger-muggery, hush of night, hush up,
   hush-hush, hushing, inaudibility, keep quiet, kill, lisp,
   lucid stillness, lull, mollify, muffle, mum, mute, muzzle,
   noiseless, noiselessness, pacify, peace, pipe down, placate,
   pour balm into, put to silence, quash, quell, quiesce, quiescence,
   quiet, quiet down, quieten, quietness, quietude, repress, rest,
   rhonchus, rock, rock to sleep, secretiveness, secretness, shush,
   shushing, shut down on, shut up, sibilance, sibilate, sibilation,
   siffle, sigmatism, silence, silent, silentness, siss, sissing,
   sit on, sizz, sizzle, sizzling, smooth, smooth down, smooth over,
   smoothen, smother, sneeze, sneezing, sniff, sniffle, snore, snort,
   snuff, snuffle, soft-pedal, soften, solemn silence, soothe,
   soundless, soundlessness, spit, splutter, sputter, squash, squelch,
   squish, stabilize, steady, sternutation, stertor, stifle, still,
   stillness, stilly, strike dumb, subdue, suppress, swish, tacitness,
   taciturnity, throttle, tomblike silence, tranquilize, tranquillity,
   wheeze, whish, whisht, whisper, whist, whistle, whistling,
   white noise, whiz, whoosh, zip