The word "invariable" refers to something that remains constant or unchanged. There are a variety of synonyms for this concept, including words like constant, unchanging, consistent, steady, and static. These words can all be used in place of "invariable" in order to convey a similar meaning. Additionally, other synonyms such as unvarying, fixed, unwavering, persistent, and inflexible can also be used to describe something that is unchanging or constant. Whether discussing a person's behavior or the rules of nature, these synonyms can help to convey the idea that something remains the same over time.