A defense of some offensive behavior or some failure to keep a promise etc. WordNet 3.0 & Open English WordNet

In American jurisprudence, an excuse is a defense to criminal charges that is a distinct from an exculpation. Wikipedia

Self-justification describes how, when a person encounters cognitive dissonance, or a situation in which a person's behavior is inconsistent with their beliefs, that person tends to justify the behavior and deny any negative feedback associated with the behavior. Wikipedia

Phenomenon where a person confronted with their hypocrisy will retroactively justify it Wikidata

An excuse, especially one used to avoid responsibility or blame. Wiktionary

Excuse. Wiktionary (translation)

That which exculpates; an excuse. Wiktionary

A defense to a criminal or civil charge wherein the accused party admits to doing acts for which legal consequences would normally be appropriate, but asserts that special circumstances relieve that party of culpability for having done those acts. Wiktionary