Ballast is a noun that refers to something that gives stability.

The origin or our word of the day is uncertain, but we know that it began as a word to describe a device used to create balance on such things as sailboats. When used figuratively, it refers to anything that provides balance or stability. For example: When she joined a workplace with so many people in their late teens and twenties, Sara needed to serve as a ballast. Because she was in her forties, she could provide the kind of stability that a younger person could not.