1. To utter words indistinctly or with a low voice and lips partly closed; esp., to grumble; to complain under one's breath.
2. To sound with a low, rumbling noise.
1. Murmurer.
2. Grommeler.
Murmurer.
A low continuous indistinct sound; SYN. muttering, murmur, murmuring, murmuration.