noun (plural alibis)
verb (alibis, alibiing, alibied)[with object] informal
late 17th century (as an adverb in the sense 'elsewhere'): from Latin, 'elsewhere'. The noun use dates from the late 18th century
The word alibi, which in Latin means ‘elsewhere’, has been used since the 18th century to mean ‘an assertion by a person that he or she was elsewhere’. In the 20th century a new sense arose (originally in the US) with the meaning ‘an excuse’. This use is a fairly common and natural extension of the core meaning, but is still regarded as incorrect by some traditionalists.