Real Dictionary

murmur
A murmur is something that is said which can hardly be heard.
verb: If you murmur something, you say it very quietly, so that not many people can hear what you are saying.

murmur in American English
a low, indistinct, continuous sound, as of a stream, far-off voices, etc.
to make a murmur
to say in a murmur
intransitive verb: to make a low or indistinct sound, esp. continuously
noun: a low, continuous sound, as of a brook, the wind, or trees, or of low, indistinct voices
transitive verb: to sound by murmurs

murmur in British English
noun: a continuous low indistinct sound, as of distant voices