Your alibi is evidence that proves your innocence. If you were making cookies with your mom when someone raided your sister's piggy bank, your mom is your alibi , since she knows you were with her when the crime was committed. Explore the term ' alibi ,' its definition , origins, synonyms, and significance in the legal context. Understand how it is used in criminal defense and everyday language. The meaning of ALIBI is the plea of having been at the time of the commission of an act elsewhere than at the place of commission; also : the fact or state of having been elsewhere at the time. How to use alibi in a sentence. Did you know? Synonym Discussion of Alibi . ALIBI definition : 1. proof that someone who is thought to have committed a crime could not have done it, especially…. Learn more.