to cook something by keeping it almost at boiling point; to be cooked in this way

to be filled with a strong feeling, especially anger, which you have difficulty controlling

She was still simmering with resentment.

She was still quietly simmering from her argument with Nathan.

to develop for a period of time without any real anger or violence being shown

This argument has been simmering for months.

The simmering dispute finally erupted.

the state when something is almost boiling

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