An Etymological Dictionary of Astronomy and Astrophysics

A claim or piece of evidence that one was elsewhere when an act, typically a criminal one, is alleged to have taken place (OxfordDictionaries.com).

Etymology (EN): From L. alibi (adv.) “elsewhere, somewhere else,” locative of alius “another, other, different,” → alias.

Etymology (PE): Enigâh, literally “other place,” from eni, from Mid.Pers. anya “other,” → alias, +gâh “place,” → time.