The word "re-vocable" refers to something that is capable of being cancelled or revoked. Its opposite or antonym is "irrevocable," which means something that is permanent, final and cannot be reversed.
For example, a revocable trust allows the creator to make changes or revoke it altogether, while an irrevocable trust cannot be changed or cancelled. Similarly, a revocable job offer implies that the offer can be withdrawn, while an irrevocable job offer suggests that it is a final and binding agreement.
Other antonyms for "re-vocable" include "non-revocable," "fixed," "unalterable," "immutable," and "permanent." These words all suggest something that cannot be changed or undone, unlike something that is revocable.