Today’s prompt immediately brings to mind something hot.
A pan left on the stove to simmer, allowing the foods to blend. The use a positive action and the literal use of the word.
It also has quite figurative uses. A person that is angry can often be said to be simmering and generally are left to cool down before further intereaction. In this case simmer is used in a more negative means.
These are essentially the first thoughts, what did the prompt bring to mind for you?