1 A claim or piece of evidence that one was elsewhere when an act, typically a criminal one, is alleged to have taken place.
1.1 informal An excuse or pretext.
verb alibis, alibiing, alibied
Provide an alibi for.
Late 17th century (as an adverb in the sense ‘elsewhere’): from Latin, ‘elsewhere’. The noun use dates from the late 18th century.
Harry had the “perfect” alibi, being in jail at the time of the robbery.