Definition of "simmer"

The locomotive was the now inevitable American 2-8-0, No. 2623. There she stood, effectively blocking the level crossing, simmering gently, massively inert. It was almost dark, and one's final sight was of her high, firelit cab, the enginemen nonchalantly leaning out, waiting for the right-away, while impatient road convoys piled up on both sides of the crossing.

1945 January and February, “Notes and News: American Locomotives in France”, in Railway Magazine, page 46

That way, the heat can circulate under the meat and prevent it from simmering in its juices.

2004, Susan Westmoreland, The Good Housekeeping Cookbook, Hearst Books, page 89

There are other easy ways you can bake and simmer and sauté wild game without qualifying as a gourmet cook.

1981, Phyllis Hobson, Easy Game Cookery, Storey Publishing, page 2

Maybe that really did happen, and Robin's anger at his wife had simmered for this long?

2006, Earl Ganz, The Taos Truth Game, UNM Press

The idea for The Sims was one that had been simmering in Wright's mind for quite some time, and was initially conceived as an architecture simulation.

2003, Mark H. Walker, Games That Sell!, Wordware Publishing, Inc., page 162