0 to speak quietly and in a low voice that is not easy to hear, often when you are worried or complaining about something:
2 a complaint that is made to only a few people:
There were mutters that other departments received more money than ours.
3 to speak quietly and in a voice that is not easy to hear, often when you are anxious or complaining about something:
He was wrong when he said he was not muttering.
Let us have no muttering under the breath.
I think that he muttered something about my having missed out the ethnic minorities.
Anybody who is willing, who has the strength, if he is muttering about it, can go and try.
Perhaps he would care to listen to me, instead of muttering under his breath.
I heard them muttering something about it yesterday.
He muttered that we did not ask him.
They imagine that, by sitting on their bottoms on the benches and muttering, they will escape.