grumble

To grumble means to complain in a low, unclear, often annoyed way. The speaker is unhappy, but not usually making a dramatic speech or starting a serious argument. Instead, the feeling comes out as muttering, quiet protest, or a rough, low complaint. For example: "The customers grumbled about the long wait," or "He grumbled when the train was late."

People can grumble directly to another person, but they often do it under their breath or to themselves. That gives the word a feeling of low-level annoyance rather than open conflict. "She grumbled to herself as she looked for her keys" suggests quiet frustration, not a full complaint meant for everyone in the room.

The word also works as a noun. It can mean a small complaint or a low sound. "There was a grumble of thunder in the distance" uses the sound meaning, while "A few grumbles came from the back of the room" uses the complaint meaning. It is useful because it connects sound and feeling: both are low, uneasy, and not fully expressed.

So, whether it is a person unhappy with a delay, a stomach making noise before lunch, or thunder rolling far away, grumble suggests something low, rough, and slightly troubled. It is a word for complaint, but also for the kind of sound that seems to carry complaint inside it.