barely audible
decrescendo
dim
distant
echoless
faint
faint-voiced
feeble
gentle
half-heard
hush as death
hushed
inaudible
indistinct
low
mousy
murmured
noiseless
pianissimo
piano
quiescent
quiet
scarcely heard
silent
soft
soft-sounding
soft-voiced
soundless
still
still as death
stilly
subdued
unarticulated
unclear
unhearable
unpronounced
unsounded
unuttered
unvocalized
unvoiced
weak
weak-voiced
whispered
whist