mutter

This word conveys a sense of suppressed emotion, typically irritation, grumbling, or secrecy. The sound is characterized by low volume and poor articulation, creating an impression of speaking into one's chest or through clenched teeth rather than projecting the voice. As a noun, it often describes a collective sound, such as a crowd's reaction, where individual words are lost in a general hum of dissatisfaction. It differs from whispering in that whispering is usually intentional for privacy, while muttering often suggests an involuntary or habitual expression of annoyance.