Irreversible
Part of speech: adjective
Definition: Incapable of being reversed or turned about or back; incapable of being made to run backward; as, an irreversible engine. Incapable of being reversed, recalled, repealed, or annulled; as, an irreversible sentence or decree. Incapable of being reversed to the original state without consumption of free energy and increase of entropy.
Example sentence: I have a statement on the Social Security. A lot of people approaching that age have either already retired on pensions or have made irreversible plans to retire very soon... I consider it a breach of faith to renege on that promise. It is a rotten thing to do.
Permanent
Part of speech: noun
Definition: A chemical hair treatment imparting or removing curliness, whose effects typically last for a period of weeks.Given an n \times n matrix a_{ij} \,, the sum over all permutations \pi \, of \prod_{i=1}^n{a_{i\pi(i)}}.
Part of speech: adjective
Definition: Without end, eternal.Lasting for an indefinitely long time.
Example sentence: The one permanent emotion of the inferior man is fear - fear of the unknown, the complex, the inexplicable. What he wants above everything else is safety.