The phrase "irreversible truth" refers to a fact or reality that is unchangeable and permanent. Synonyms for this phrase include "undeniable reality," "unchangeable fact," "irrevocable truth," "immutable certainty," and "permanent verity." These words indicate that the truth being referred to is absolute and cannot be altered by any means. They suggest that the truth is beyond dispute and cannot be reversed or changed in any way. Using these synonyms adds weight and certainty to any statement or argument that relies on a fundamental truth or fact that cannot be disputed or negated.