Synonyms for Quiet (same or very similar meaning)
WordNet sense 1 (a period of calm weather):
lull
WordNet sense 2 (an untroubled state; free from disturbances):
tranquility, tranquillity
WordNet sense 3 (the absence of sound):
silence
WordNet sense 4 (a disposition free from stress or emotion):
placidity, repose, serenity
WordNet sense 5 (become quiet or quieter):
hush, quiesce, quieten, pipe down, quiet down
WordNet sense 6 (marked by absence of sound):
silent, soundless, still
WordNet sense 7 (not showy or obtrusive):
restrained
WordNet sense 8 (not ostentatious):
unpretentious, unostentatious, unpretending
WordNet sense 9 (marked by a state of tranquil repose):
quiescent
WordNet sense 10 (make calm or still):
tranquilize, tranquillize, tranquillise, calm down
WordNet sense 11 (in a softened tone):
hushed, muted, subdued
WordNet sense 12 ((of sound) relatively low in volume):
soft
WordNet sense 13 ((of a body of water) free from disturbance by heavy waves):
placid, smooth, tranquil, unruffled
WordNet sense 14 ((of weather) free from storm or wind):
calm
WordNet sense 15 (with little or no activity or no agitation (`quiet' is a nonstandard variant for `quietly')):
quietly
From the ODE community, based on WordNet
add/edit