Murmur is a word that can be used in various contexts, such as describing a low and indistinct sound, a whisper, a soft speaking voice, or the sound of a babbling brook. There are several synonyms for the word murmur, including whisper, mumble, utter, mutter, grumble, rumble, and hum. A whisper is a hushed or quiet mode of speaking, while a mumble is an unintelligible or unclear utterance. Utter is a general term used to describe any spoken or written words, whereas mutter refers to speaking under one's breath. On the other hand, grumble denotes a low and discontented sound, while rumble and hum are more commonly used to describe sounds made by large machinery or engines.