Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. If a change is irreversible, things cannot be changed back to the way they were before. irreversible definition in English dictionary, irreversible meaning, synonyms, see also 'irreversibly',irreversibleness',irrepressible',irreversibility'. Definition of 'irreversible' Word Frequency. Irreversible definition, not reversible; incapable of being changed: His refusal is irreversible.