1) Final and unalterable 2) French word used in English 3) Irreversible 4) Irrevokable 5) Sealed 1) Irreparable 2) Irreversible 3) Irrevokable 4) Permanent 
• (a.) Incapable of being recalled or revoked; unchangeable; irreversible; unalterable; as, an irrevocable promise or decree; irrevocable fate.
Ir·rev'o·ca·ble adjective [ Latin irrevocabilis : confer French irrévocable . See In- not, and Revoke , and confer Irrevocable .] Incapable of being recalled or revoked; unchangeable; irreversible; unalterable; as, an irrevocable promise or decree; ir...
final and unalterable 
[adj] - impossible to retract or revoke
irrevocable 1. Impossible to revoke, to undo, or to change. 2. That which is impossible to retract or to revoke.
irrevokable adjective incapable of being retracted or revoked; `firm and irrevocable is my doom`- Shakespeare
Cannot be revoked, withdrawn or cancelled except by mutual agreement of the parties. Particularly applies to Letters of Credit.
not to be revoked or recalled; unable to be repealed or annulled; unalterable: an irrevocable decree.