al ‧ i ‧ bi /ˈæləbaɪ, ˈælɪbaɪ/ BrE AmE noun [countable]
[ Date: 1600-1700 ; Language: Latin ; Origin: 'somewhere else' ]
1 . something that proves that someone was not where a crime happened and therefore could not have done it
a perfect/cast-iron/unshakeable etc alibi
He had a perfect alibi and the police let him go.
2 . an excuse for something you have failed to do or have done wrong