What are the opposite words for un-stabler?

Unstable is a word that suggests something is not firm or steady. The antonyms of un-stable are stable, secure, certain, steady, fixed, constant, and reliable. Stable comes from the Latin word 'stabulum', which means a place for standing. Stable implies the internal consistency of something and not being easily changed. Secure is another antonym that means something is not likely to be at risk or feel uncertain. Certain is used to mean something is definite or positive. Steady indicates something is not changing much, while fixed is used to describe something that is firmly established or settled. Constant is used to indicate something that keeps going or is reliable. Reliable is something that can be depended upon.