The word "un-changeable" refers to something that cannot be altered or modified. Its antonyms or opposite words are "changeable," "modifiable," or "adaptable." These words refer to an ability to alter or adjust something. For example, if you say that a plan or a decision is changeable, it means that it can be altered if required. On the other hand, if you say that something is un-changeable, it signals that it is predetermined, unalterable, or set in stone. It's essential to be aware of these antonyms to express yourself precisely and effectively while communicating with others.