1. In law, a form of defense whereby a defendant attempts to prove that he or she was elsewhere when the crime in question was committed: An alibi is the fact of having been elsewhere when a crime in question was committed.
2. An explanation offered to avoid blame or justify action; an excuse: As an alibi, Mark told his mother that he was helping the neighbor and that was why he didn't finish his homework for school.

1. To make an excuse for oneself: Tom allied or justified the fact of not doing him homework to his teacher, because he had to go to the hospital the day before.
2. To make an excuse for another person: Mary alibied her daughter's absence from school by writing a note to the teacher saying that she was sick and had to stay in bd..