[1] : WordNet (r) 2.0

keep quiet
     v : refrain from divulging sensitive information; keep quiet
         about confidential information; "don't tell him any
         secrets--he cannot keep his mouth shut" syn: shut
         one's mouth, keep one's mouth shut ant: spill the
         beans
see also:
shut one's mouth keep one's mouth shut spill the beans 

[2] : Moby Thesaurus II by Grady Ward, 1.0

33 moby thesaurus words for "keep quiet":
   abide, be mute, be silent, be still, coast, forswear speech,
   freeze, keep mum, keep silent, keep still, lie still, make no sign,
   mark time, not breathe, not stir, play dumb, remain,
   remain motionless, repose, rest, say nothing, shut up, stand,
   stand fast, stand firm, stand mute, stand still, stay, stay put,
   stick, stick fast, tarry, tread water

Keep >> K Words
Keep, definition of term: Keep
keep_pag1.html

Keep Up >> K Words
Keep Up, definition of term: Keep Up
keep+up_pag1.html

Keep Off >> K Words
Keep Off, definition of term: Keep Off
keep+off_pag1.html

Keep Back >> K Words
Keep Back, definition of term: Keep Back
keep+back_pag1.html

Keep Away >> K Words
Keep Away, definition of term: Keep Away
keep+away_pag1.html

Keep Down >> K Words
Keep Down, definition of term: Keep Down
keep+down_pag1.html