The word "unreversible" means something that cannot be reversed or undone. Its antonym would be a word that means something that can be undone or reversed. Some possible antonyms for "unreversible" are "reversible," "undoable," "fixable," "correctable," "malleable," and "amendable." For example, if a mistake is made, it can be corrected or fixed, which means it is not irreversible. Similarly, if a decision is made, it can be amended or changed, which means it is not irreversible. The concept of reversibility is important in many fields, including science, engineering, medicine, and law.