The word "unvariable" refers to something that cannot be changed or altered. However, there are many synonyms that convey the same meaning, such as unchanging, constant, invariable, fixed, immutable, steadfast, stable, rigid, unwavering, and consistent. Each of these words denotes a characteristic of something that remains the same, despite any external circumstances or events. Whether it's an unchanging routine, a steadfast belief, or an immovable object, there are many words to describe something that stands the test of time without faltering. Choosing the right synonym depends on the context of the sentence and the tone of the conversation.