inert

An inert substance or thing doesn't change, move, or react much. Think of a rock that's been sitting in one place for years.

Inert is often used to describe things that are stable and don't easily change. In chemistry and science, an inert gas might not combine with other elements because it's not very reactive. People also use the word when talking about objects or situations where nothing much happens - a room full of old furniture can be inert if it hasn't been touched in years. Sometimes "inert" is used to describe people who are calm and quiet, but this isn't as common.